Uh huh bro. 3rd party characters branch out to Smash Noobs. If they see Megaman in Brawl and have never played Smash a day in there life, then you know good and well they'll pick up a copy. Perfect example: Lots of MGS fans thought smash at first was a kids game, but now, ohhhhhh baby, with the inclusion of Snake, it's now a mans game!
Dude, my cousin is a huge MGS fan, and once he heared of Snake making a appearance in Brawl, he played Melee. In which, his two younger brothers played Melee a lot. Because of that, he is now a average casual smash fan. I can just imagine it with Sonic. It'd be like that times 5. With Mega Man, it'd be like that times 2. Simplpy put, all-stars in one game attract gamers and non-gamers. Them fighting together and against each other all at once is pure nogstalia. It gets you excited. It's the things people dream of-and Sakurai is making it. Megaman is the biggest dream character not confirmed in Brawl yet (not including veterans; specificlally one in green overalls).
Just ponder that for a second. If Sakurai was to make Brawl without Megaman, with Snake and Sonic, he would be making a GRAVE mistake. He's got the 1st and 3rd most reconizable 3rd party characters, but not the first. And never forget the much awaited "end", where Sakurai will reveal what is left in Brawl-mainly the last part of the roster. I have a feeling, we could see a 3rd party character there. *cough Mega Man, Geno, or both cough*