In an RPG with a party of characters, I'll build up strengths of each individual character but in an action-adventure type game where you control a single protagonist, I'll usually choose to learn a new ability/skill/weapon rather than upgrade an existing one, if only to find out how it works. Though I suppose I still eventually always find one or two things that work better or that I prefer using, so by the end of the game, I've still got a fairly lopsided skill tree.