To note, I think Marth should be a Starter. Same with Ness for sure. I wouldn't mind if Jigglypuff and Falcon are kept Starters too. I am unsure of with Luigi, but the original 12 being permanent Starters is cool with me. Also, if a series gets more characters, the Veterans of that series should be Starters, imo. Or at least the first among them(as in Marth, Ness, Pikachu, Jigglypuff, the Zelda characters do that already(in the way I want it), any 3rd party if a Company gets more than one character somehow, Falcon(but only if F-Zero gets a new rep. He can be either/or otherwise), Mario, Bowser, Peach).
I honestly rarely bother to go through Single Player unless it's super fun and just for the unlockables. Brawl... kind of dropped the ball on this outside of the SSE, but it'd take me forever to say why I wasn't fond of the single player all that much. I'll keep it brief; I love unlocking characters. You can't erase them on Brawl so you can do it again. You only unlock them once through any of the means. I think this is a design flaw that 4 should fix.