The more I think about it, I'm really excited to see how the broader gaming public takes to the demo. Obviously they'll be naysayers, but with a chance to go hands on with it themselves I think the dynamic could change quite rapidly.
Melee's still a lot of fun, and Project M should remind some people of that. That's already a great thing. But I think with Brawl's presentation & new retro stages (and the balance changes, if noticed), even more will see Project M as something that stands on its own. Furthermore, things like the L-cancel flash could really encourage them to learn Smash in a way they haven't before. Unlike 64 or Melee, it won't be hidden so much as an easter egg for those 'in the know.'
Mostly, I'm looking forward to Project M being judged for what Project M is, not what Melee or Brawl were. Exciting stuff.