I almost think the limited pool of the Japanese stuff may even be more of a draw for me, if I were to delve into 6" scaled stuff at all. I'd almost prefer that than the temptation of a more elaborate line like Hasbro's going to churn out. Still, you never know how obscure some of the stuff could get from Japan. So far it's all been safe bets though, from any of it. It's still so new.
I like the Hasbro stuff, actually, and have been tempted at times. It's got flaws, but overall I think it's got some nice stuff even with the "cellulite". I actually bought my first (and only) 6" figure they make tonight, as I happened upon a Bossk at a Wal-Mart. Since I like all things Bossk, I caved. He's got some ugliness like the knee pins, and the mismatched yellow, but otherwise he's pretty neat.
But if I were to add a whole 1/12 collection, I'd prefer to go the higher end route ultimately. And the pics seem to imply the two don't jive real well scale-wise either so I'd not want to mix them either. I think if that were possible I'd be even more tempted, actually.