^Hey, we'll take another vote for Robert Conrad!
And if they'd also done a first pilot with its own cast...Jack Lord as Christopher Pike.
I'd go with Martin Landau as Spock, BTW. Having trouble thinking of a good Scotty offhand, but there must be tons of character actors from the period who would have done him justice. For some reason Dan Blocker keeps popping in my head, but he already had a regular gig on a much bigger TV show at the time....
Warren Stevens would be another possibility for McCoy...maybe even Spock.
And if they needed a character to take over on helm or navigation when Sulu or Chekov weren't on the bridge, it would be pretty cool to see Martin Millner flying the ship. Perhaps a regular security chief by day...?