I always thought Morgan Freeman should be playing a Vulcan. Tuvok's father, for example.
Heck, I would've rather seen Morgan Freeman play Tuvok. Tim Russ did a good job, but I always regretted that they weren't able to go the route they intended and cast him as more of a venerable elder/mentor type.
I also regret that they never got the late Roscoe Lee Browne to play a Klingon.