Nurp
Well, actually, you could add some kinda currency thing so you can unlock new classes or whatever, or unlock different skills, but make everything still balanced. Like, for say, if you reach 'level 3' on fighter (Probably level by winning, dunno) you can unlock the ability 'Rage' which would be like, roll 2d10 and deal that much damage ignoring armor but take double damage or whatever, I dunno.