Deathsmiles is an awesome game, I was lucky to get a preorder in for the LE before they closed, apparently they really underestimated demand on it. I can imagine the LE jumping in price like the Senko LE did. Deathsmiles 2 comes out pretty soon in the arcade, although it looks kind of...eh...I'll play it before I judge it.
Anyway, Mega Black Label adds a lot to the game, although it might not be noticeable if you don't play hardcore. Besides the additional character and stage (which by itself is pretty major), it changes the balance of the game and adds a new difficulty level that greatly makes up for the people who thought the core game was too easy. There are tons of smaller changes as well, it's definitely worth getting.