I agree with your fourth idea. It would add almost a momentum factor to the fight- The better you fight, the higher your stats.
I actually have another idea- a luck factor. This too would be affected by your momentum-style points. Simply put:
There is a small possibility that attacks will miss you or your attacks will miss your opponent. Again, this is affected by your points.
Also, when your luck is high, your attack range increases slightly (especially for, say, Zelda's lightning foot, which needs to be placed precisely for decent damage), and you can (on very rare occasions) even get a piece out of opponents who have otherwise dodged your attack.
However, if your luck is bad, attacks will more likely miss and dodges harder to perform.
Luck is a temporary thing, and will dissipate over time. Luck is affected by accuracy and strength of your attacks, your style points (as compared to other fighters), and how long you can keep alive before getting KO'ed.
Otherwise, the Adventure per character need not be that specialized (most characters, minus secret characters, already have specific stages in the Adventure mode).
For the Human fighter idea, I have an alternate solution- a complete career mode where you can build your character from the ground up. There are generic and specialized techniques that can be learned by buying items using skill points. The character can be human or non-human. The overworld similar to Mario Golf GBA (with more relevant graphics) would add flavor to the brew, but it would not be necessary.
Before anyone asks, this is my opinion on SSB on the DS- Isn't happening. The game, no matter how well done, will not work without a joystick. Then again, I thought the same of SM64x4(DS), but am hearing otherwise.
Too many numbers...
