Ha! This is a Nintendo game, for Mario characters, the word 'enough' means nothing. Anyway. Why should anyone complain about the distribution of Mario series characters compared to Zelda series, Fire Emblem, etc. Because of the supreme amount of Mario games, There is a huge roster of potential Mario characters that could be available for SSBB.
Here is my list of potential Mario characters with reasons why they would be good:
1) TOAD - The sentient, bipedal, fungus should join the world of fighting. I can see him using his head effectively. And also backflips and turnips. Also, anyone ever heard of Prince Mush (all you hardcore Paper Mario veterans know who I'm talking about.) 'nuff said!
2) KAMMY - Floats like Peach; long ranged, magical grabs (kinda) like Mewtwo and spell spamming. With Kammy, I see potential. Kammy pros will rack up damage with long ranged attacks, and then come up and smash said opponent into doom with that long wand. Oh yes, I would love to see her in.
3) PAPER MARIO - Hammer, spin jump, tornado jump, hammer throw, etc. With some of his previous badge moves at his disposal, he would become a force to be reckoned with, replacing the good doctor, and very DIFFERENT from Mario. Play the game - You'll see!
4) HAMMER/FIRE/BOOMERANG BROS. - Ice Climber style, with different costumes for each weapon.Traditionally, hammer bros. appear in pairs, and thus would they, in SSBB. I needn't even start with movesets. I think you can guess.
5) BOWSER JR. - Paint, shadow Mario. This has been explained. I needn't say anything.
6) DRY BONES - Gasp! I hear you cry - a generic character. Who cares, I chant back in unison. His weapon is a bone club(/unlimited supply of bone clubs). The moveset writes itself.
7) BIRDO - Oh Wow! She fires eggs, she sucks people in (Kirby - style), she fires them out! Also, she has alarge head and tail at her disposal. Yay!
8) BOO - Or perhaps a Duplighost (look at the avatar). I see floating; I see invisible shielding; I see (with Duplighost) turning into opponent character at the touch of a button (WOW! Awesomeness!); Also biting, punching, slapping. I see Boo/ Duplighost pwnness.
More generic characters. Anyway, some of you may be thinking 'omg no, this n00b has forgotten Geno/Boshi/Square character. But Geno/etc. pwns. LOLXORS!!!111. This guy's a n00b!1'. Well I say 'Bah' unto ye. Super Mario RPG was made by Square and SUCKS compared to any other Mario game. Anyways, Fin