No I don't agree. The whole point of Super Smash Bros is that it is like a celebration of Nintendo and too many non-Nintendo characters would spoil that. I think Nintendo agrees because in one of the interviews on their website they talked about how they had to be careful about where to draw the line in Super Smash Bros Brawl.
I think that any third party characters in the game must be very famous. Sonic and Solid Snake are both very famous so it is okay to have them in. Megaman might be just about famous enough I'm not really sure.
Mostly Everyone has Heard or Seen Megaman in there Lives.
I think He would have a Chance of Getting in There.
I think Banjo-Kazooie would be a Good Character to put in there too.