It's such a shame Star Trek didn't continue with the cast from The Cage.
Is it really a shame? The network rejected them because a) they weren't really very interesting for the most part and b) they were all-white, despite Roddenberry's promise to satisfy the network's desire for ethnic diversity. Would Trek have been so influential and culturally significant if it had presented a lily-white version of the future, with maybe a few token minorities in the background here and there?
Jeffrey Hunter and William Shatner were basically playing the same character to start with -- early Kirk was written all but indistinguishably from Pike -- but Shatner brought a warmth, humor, and accessibility to the role that Hunter didn't. Similarly, John Hoyt was playing the same character as DeForest Kelley aside from the name, but Kelley was the actor Roddenberry had wanted in the doctor role all along; he just didn't manage to get him until the third try.
As for Number One, not to disparage Majel Barrett's acting, but I'm not sure it would've been good for the show or the actress for the leading lady to be the showrunner's mistress. Even aside from the possible scandals, it might've led to Roddenberry being too indulgent of her or not pushing her hard enough as an actress. And it could've led to strife among the cast if it was felt that she was getting special treatment. As for Nimoy, he could very well have still been the breakout star for the same reasons as in reality, and then there could've been internal strife about whether Spock or Number One should be the more prominent character.
As for the rest, Peter Duryea was kind of dull, and I can barely even remember the guy who played Garison. They didn't seem to have a chief engineer, a role that would soon become essential.
I would've been okay with them keeping Goodwin as Colt; I liked her more than I ever liked Rand. But then it would've been unfeasible to present the events of "The Cage" as something that happened 13 years earlier.