Theme: Stay on the right track ~ or ~ We are well trained.
This is best explained by starting with the unifier.
59A. Engineer, brakeman and conductor ... and what the ends of the answers to starred clues comprise?: TRAIN CREW. Those named professionals are indeed the CREW of a TRAIN. The theme answers will make a TRAIN CREW of a different sort.
16 A. *Person to emulate: ROLE MODEL. This is the person who is a standout at what s/he does, performing at the highest level, getting the most done, and showing the right way to do it. A MODEL TRAIN is a scaled down representation of a real TRAIN, used in the hobby of Rail Transport Modeling, which can be extremely elaborate and realistic.
23 A. *Thanksgiving condiment: TURKEY GRAVY. Gravy is a sauce often made from the juices of meat - in this case, TURKEY, that run naturally during cooking and often thickened with wheat flour or corn starch for added texture. It is typically served in a GRAVY boat. The GRAVY TRAIN is a situation where one can make a great deal of money with very little effort.
35. *Effective remedy with little downside: MAGIC BULLET. A medicine or other problem solving remedy, especially one newly discovered or unexpected with wonderful or highly specific properties. A BULLET TRAIN is a high speed passenger rail transport that uses an integrated system of specialized rolling stock and dedicated tracks. They run at least 160 miles per hour, and some systems exceed 200 miles per hour.
50 A. *A high-profile trial might become one: MEDIA CIRCUS. This is any news event that attracts coverage that is excessive in degree and/or duration, or out of proportion to the event being covered. This is often also magnified by sensationalistic reporting. A CIRCUS TRAIN is transportation to take a CIRCUS company from one venue to the next.
8. Aromatic herb: SAGE. Salvia officinalis is a perennial, evergreen subshrub, with woody stems, grayish leaves, and blue to purplish flowers. It has a long history of culinary and medicinal use.
12. Church divide: AISLE. The passage between the rows of seats, benches or pews.
14. Rapping MD?: DRE. Andre Romelle Young [b. 1955,] known professionally as Dr. Dre, is an American rapper, record producer, audio engineer, record executive, entrepreneur, and actor. He is the founder and CEO of Aftermath Entertainment and Beats Electronics,
15. Mariano Rivera's record 652: SAVES. Mariano Rivera is a Panamanian-American former professional baseball pitcher who played 19 seasons in Major League Baseball for the New York Yankees, from 1995 to 2013. Nicknamed "Mo" and "Sandman", he spent most of his career as a relief pitcher and served as the Yankees' closer for 17 seasons.
19. Wavelike pattern: MOIRE. A large-scale interference pattern that can be produced when an opaque ruled pattern with transparent gaps is overlaid on another similar pattern. For the moiré interference pattern to appear, the two patterns must not be completely identical, but rather displaced, rotated, or have slightly different pitch. [Wikipedia]
20. "Eighteen Wheels and a Dozen Roses" singer Kathy: MATTEA. Kathleen Alice Mattea (b. 1959) is an American country music and bluegrass singer. Active since 1984 as a recording artist, she has charted more than 30 singles on the Billboard Hot Country Songs charts, including four that reached No. 1.
26. Nigerian pop star: SADE. Helen Folasade Adu [b 1959] known professionally as Sade Adu or simply Sade [pronounced Shad-day, don't ask me why] was born in Nigeria, but brought up in England. She has had an enormously successful career.
29. Notable times: ERAS. Jazz, for example
30. Summer beverage: ICE TEA. Brewed TEA served over ICE. Let the ICE - ICED controversy commence.
33. "__ Tu": 1974 hit: ERES.
40. Trickeries: FRAUDS. Fakes, phonies, shams.
43. Tel __: AVIV. Tel AVIV Yafo, to be complete, is a city on Israel's Mediterranean coast with a population of 460, 613.
47. Brown and blonde: ALES. Less hoppy than IPAs.
49. Cream or Nirvana: TRIO. Groups of three musicians.
54. Red Sox rivals, on scoreboards: NYY. New York Yankees.
55. Literally, French for "again": ENCORE. Makes sense.
56. Perot of politics: H ROSS.
64. Carrier to Tokyo: ANA. All Nippon Airways Co., Ltd is Japan's largest airline.
65. Hotel patron: GUEST. Paying customer.
67. Time out?: NAP. "Out" meaning asleep.
68. Palm gadgets, briefly: PDAS. Personal Data Assistants. Mobile devices which function as personal information managers. Now pretty much displaced by muti-functional smart phones.
Down:
1. Swiss river: AAR. A tributary of the High Rhine and the longest river that both rises and ends entirely within Switzerland. Its total length from its source to its junction with the Rhine comprises about 295 kilometers (183 mi.)
2. Corp. tech exec: CIO. The Chief Information Officer is the company executive responsible for the management, implementation, and usability of information and computer technologies.
3. Internet connector via phone line: DSL MODEM. Digital Subscriber Line is a family of technologies that are used to transmit digital data over telephone lines. A modem – a portmanteau of "modulator-demodulator" – is a hardware device that converts data from a digital format.
7. Disney frame: CEL. A special or limited edition version of artwork from an animated cartoon.
8. "No Exit" dramatist: SARTRE. Jean-Paul Charles Aymard Sartre ]1905 –1980] was a French philosopher, playwright, novelist, screenwriter, political activist, biographer, and literary critic.
9. Personal user pic: AVATAR. An electronic image that represents and may be manipulated by a computer user.
10. Lake on the French/Swiss border: GENEVA.
11. Op-ed pieces: ESSAYS.
13. Send out: EMIT. As, frex., radio waves or light.
15. Alone, at a party: STAG.
17. Christian sch. in Tulsa: ORU. Oral Roberts University.
20. Whitman "53-Down" subject: MYSELF. SONG of MYSELF is a poem by Walt Whitman (1819–1892) that is included in his work Leaves of Grass. It has been credited as "representing the core of Whitman's poetic vision."
21. 23rd of 24: PSI. Psi (Greek) (Ψ, ψ), the 23rd letter of the Greek alphabet. In both Classical and Modern Greek, the letter indicates the combination /ps/ (as in English word "lapse").
24. Company with spokes-elves: KEEBLER. They make cookies.
31. Star quality?: EGO. Quality - I'm not so sure. More precisely, a characteristic.
32. The Red Baron, for one: AIR ACE. A flying ace, fighter ace or AIR ACE is a military aviator credited with shooting down five or more enemy aircraft during aerial combat. Manfred Albrecht Freiherr von Richthofen [1892-1918,] known in English as the Red Baron, was a fighter pilot with the German Air Force during World War I. He is considered the ace-of-aces of the war, being officially credited with 80 air combat victories.
34. Canon initials: SLR. Single Lens Reflex, a type of camera.
36. Colombian metropolis: CALI. Santiago de Cali, or CALI, is the capital of the Valle del Cauca department, and the most populous city in southwest Colombia, with 2,227,642 residents.
37. Have: EAT. Consume.
38. Gets embarrassed, maybe: TURNS RED.
41. Tinkerer's abbr.: DIY. Do It Yourself.
42. Versatile bean: SOY.
43. One-celled critters: AMEBAS. Unicellular organisms which have the ability to alter their shapes, primarily by extending and retracting pseudopods.
44. Rome's Via __: VENETO. One of the most famous, elegant, and expensive streets of Rome, Italy. The street is named after the Battle of Vittorio Veneto (1918), a decisive Italian victory of World War I.
46. Members of string 49-Acrosses: VIOLAS. Remember, 49 A was a musical trio. Violas are the alto voices of the viol family, pitched a fifth below the violin, and an octave above the cello.
52. Sch. with a Providence campus: URI. University of Rhode Island.
53. Tune: SONG. Melody. We have a few today.
57. Atlantic food fish: SCUP. The scup (Stenotomus chrysops) is a fish which occurs primarily in the Atlantic from Massachusetts to South Carolina. Along with many other fish of the family Sparidae, it is also commonly known as porgy. First I've ever heard of it.
61. That, to Pedro: ESA. Spanish
62. Pkg. measures: WTS. Weights.