I love minis. The first time I actually used them in a game, it was like an amazing epiphany - suddenly, my players couldn't argue about where they were actually standing, vs. where their foes were actually standing, in combat situations. Later, when I started painting minis, I found that a particularly good paint job would help inspire my characterization of an NPC, spark my imagination about an organization or group in the game world, etc. In RL terms, painting is a relaxing hobby that I can do while watching TV, chatting with my wife, or really doing anything that does not require the use of my hands.
I'm not a huge fan of prepainted minis, but I don't think there's anything wrong with them.