Yeah, Brawl sold poor because no Miis. Best selling numbers for a fighting game right?
...I can't decipher this post, sorry. Can't even tell with side your on.
The idea of having your own avatar be playable is very appealing to a lot of people. Especially if said avatar are the Miis, which are everywhere.
Can we stop calling people "casuals", though? How are they any different from you and me?
OK, lets put Brawl's roster in. No need for newcomers, they didn't factor in Brawl's sales.
Yes, but are Miis a game seller? Here, they're pratically hated. Do you have some unknown means of contacting millions of nintendo fans, who resound "We want Mii!"? You say I'm generalizing, but you're generalizing even more.
You also have to consider this isn't Mario Kart. Having an avatar in a fighting game is more difficult. Anecdotal evidence time. I can't see my little brother playing a Mii with a set moveset. His favorite characters are Pit and Meta Knight, both aerial fighters with a sword(s). No other character comes close to his playtime with those two. Miis are most likely not going to be like that. I imagine the novelty of playing as himself will wear off rather quickly he finds the character less enjoyable.
But, let's say Miis are completely customizable. Will his Mii be able to pull off stuff similar to Pit and MK? If not, did Sakurai do a poor job of implementing Miis? Creating an avatar character in a fighting game is a huge, difficult investment. I would not be surprised at all if they decided it wasn't worth that effort.