Will a 30-30 kill a black bear -- sure it will, and many dead bears can vouch for this, but it would not be my choice for a hunt if I could afford a rifle in a caliber that would give me more of an edge. Is a 30-06 necessary for black bear? No, but imo it is one of the more flexible, all around calibers out there today, and it will do the job on most North American animals. Same with the .308. If it were me going on the hunt, I'd probably carry my Savage 99 in .300 Savage, as it is lighter than my 30-06.
Don't get me wrong, I like the 30-30, and think that it is currently an underrarted round, but it is the minimum I'd choose for black bear. If you go with the 30-30, one thing you might look into is the Buffalo Bore ammo, sort of a 30-30 +P, supposed to boost it's performance. I have not tried it myself, however, but have been considering ordering some just to play with.