I say put out a few classes in S&P, and then collect them later on in a single volume with some added padding and fluff (and decent artwork!). That way the die-hard fans get something new every month or two, and the bundled release can then be used to draw in new players. Besides, a lot of gamers I know have a strong "anti-hero" streak in them - publishing a "Villians of Magnamund" would be akin to a D&D Monster Manual, with everyone clamouring to play this or that class (gods know I have been wanting to play a mind flayer for YEARS...)