Theme: Heeere's Johnny - Four in fact whose last name begin the in language themes and a grid spanning reveal.
17A. One may spoil the whole bunch : ROTTEN APPLE. Johnny Rotten - The stage name of the lead vocalist for the Sex Pistols, an English punk rock band that formed in London in 1975.
24A. State capital near the Comstock Lode : CARSON CITY. Johnny Carson - Needs no intro. Carson City is the capital of Nevada.
38A. Handy guy to have around, or a hint to this puzzle's theme found in 17-, 24-, 50- and 62-Across : JOHNNY ON THE SPOT
50A. Monetary assets : CASH IN HAND. Johnny Cash - The man in black. Video(3:09).
62A. Substitute player : BENCH WARMER. Johnny Bench - Baseball catcher for the Cincinnati Reds from 1967 to 1983, not a bench warmer.
Heeere's Argyle. "I feel a hot wind on my shoulder
And the touch of a world that is older" - Mexican Radio.
My first look at the NW corner had me checking the day. Some of the clues/entries are from an older time. I felt an international feel for it, too. The anon who complained about abbreviations won't like it, but after all was said and done, I did.
1. Set in motion : STARTED
8. Letters for an open schedule slot : TBA. (to be announced)
11. LAX calculation : ETA. (estimated time of arrival)
14. Soho "So long!" : "CHEERIO!"
15. "Still and all ..." : "YET ..."
16. Fish-fowl connector : NOR
19. No. that's zero at the equator : LAT. The number for the latitude at the equator is 0 and 90 at the poles.
20. Golfer Palmer : ARNIE
21. Store, as a hose : COIL
22. Get wise with : SASS
23. Plaintive sound : MOAN
26. Economist Smith : ADAM. The Wealth of Nations, 1776.
28. Old draft classification : TWO A. Occupational deferment category.
29. Gaza Strip gp. : PLO. (Palestine Liberation Organization)
32. "__ Sleep, for Every Favor": old hymn : ERE I. Instrumental on the organ at Eccles Congregational Church, Salford, England, near to Liverpool.
34. 1950s WMD : H-BOMB. (weapon of mass destruction, WMD)
42. Margaret Mead subject : SAMOA. Her book, Coming of Age in Samoa.
43. Besmirch : SOIL
44. Drag behind : TOW
45. A or Jay, e.g. : ALer. (baseball)
48. "Jesus __": shortest Bible verse : WEPT
54. Dost own : HAST
58. Weight on one's shoulders : ONUS
59. Carries out : DOES
60. 19th-century German poet Heinrich : HEINE. Wikipedia article.
61. Genetic letters : RNA
64. Soho sir : GUV. Informal British for governor.
65. Philanderer : CAD
66. Syrian's neighbor : ISRAELI
67. Suffix with infant : ILE. (infantile, like some anons)
68. Pitcher's stat : ERA
69. Beats, and how : PUMMELS. Don't confuse with pommel horse.
1. "Get outta here!" : "SCRAM!"
2. Exhaustive, informally : THORO. (thorough)
3. Humana rival : AETNA. Health care companies.
4. Light-sensing eye part : RETINA
5. Mimosa, for one : TREE. The alcoholic drink is so called from its yellowish color, which resembles that of the mimosa. Who knew?
6. A, in Augsburg : EIN. Today's map of Germany.
7. Appear on screen like Hitchcock : DO A CAMEO
8. Data entry pro : TYPIST
9. Deep roar : BELLOW
10. Gobbled down : ATE
11. China's Zhou __ : ENLAI. First Premier of the People's Republic of China.
12. Salute with a raised glass : TOAST
13. La-di-da : ARTSY
18. "Un momento, __ favor" : POR. Yo no hablo español.
22. Signs of healing : SCABS
24. Grant with an Honorary Award statuette : CARY. Grant was given an Honorary Oscar at the 42nd Academy Awards in 1970. Frank Sinatra presented Grant with the award, "for his unique mastery of the art of screen acting with the respect and affection of his colleagues". (Wiki)
25. Caution to a game show audience : "NO HELP!". Unless it's "The Price is Right". All that help is no help.
27. Mount McKinley's national park : DENALI
29. Jammies : PJ's
30. Mauna __ : LOA. Are you nuts?
31. Resistance unit : OHM
33. Shoo-__: easy winners : INs
35. Make up one's mind : OPT
36. __ goo gai pan : MOO. Now, how do they say it in Boston?
37. Incidentally, in IMs : BTW. (By The Way)
39. Whose ark it was : NOAH'S
40. County subdivision : TOWNSHIP
41. Zipped along : HIED
46. Make beloved : ENDEAR
47. Beach Boys title girl : RHONDA. She was helpful.
49. Aries : THE RAM
50. Welsh dog : CORGI
51. Invalidate : ANNUL
52. Smoothly polite : SUAVE
53. Nuclear agcy. formed under Truman : AEC. (Atomic Energy Commission)
55. Pop singer Mann : AIMEE. Not my cup of tea but here is a video(3:12).
56. Fishhook connector : SNELL. Here, if you want to tie your own hook on the line. Most people buy hooks with the leader already attached.
57. Garr and Hatcher : TERIs. Unable to find a photo of the two of them together.
60. "No __, no foul" : HARM. Nor fish.
62. Pre-A.D. : BCE. (Before Common Era) If you need more, Wiki link.
63. Sch. with a Vancouver campus : WSU. (Washington State University)