I just saw Toshiro Mifune in something the other night, and immediately flashed on the stuff about Mifune being the Klingon Captain opposing Spock, according to Kaufmann in a little book, I think it is called best sf films never made. I've never felt good about the idea of doing 3/4 of a trek movie w/o Kirk (witness GENERATIOINS), but I gotta say, I'd've been first in line for this one.
Toshiro Mifune as a Klingon would've given as, imo, a better and more nuanced Klingon than what we ended up in latter Treks. Less over the top, Norse-Viking and more subtle, subdue Samuri-like. It would've been, to borrow Gowron's phrase, "glorious."
I have to agree with you on a movie featuring Spock heavily and Kirk less. As Nimoy has pointed out in several interviews, the character of Spock works best when he has the character of Kirk and Shatner's energitic performance to work against. In Mark A. Altman's book Captain's Log
, he quotes Nimoy from another source as saying that Spock isn't sucessful when he is left in command by himself like in "The Gaileo Seven."