Would just like to say I agree with you all on the whole 'character unlocking' concepts. Something between Melee and Brawl in difficulty would be ideal.
For example, I played Melee like a madwoman and I had no idea Game and Watch was in that game until about two years ago (this due to the fact that I deleted all the data every few months like the stupid kid that I was but still).
In Brawl the only time I ever saw the challenger approaching! screen was with Ness, who I believe took a whopping 10 versus matches to unlock? Everyone else was unlocked through SSE, in the span of two days.
Also loving the special unlock ideas, particularly the Yoshi example. That would be so boss. Maybe this should go on to stages too; an idea, there's a portion of SSB4's Adventure Mode that's reminiscent of Donkey Kong, with barrels falling down platforms and such. Beating this level in a fast enough time (not some unthinkable, pro speed-run speed, but y'know, reasonably fast) with Mario results in the unlock of 75m. Or something. Now that I think about it, that's a really lame example, but...;;
Now I'll shut up and go back to lurking. Keep those gears turning people, your thoughts amaze me~.