My students and I have had a lot of success lately with Happy Fingers--playing a piece (or a section) on the violin with the idea that the fingers are really excited to go in their spots, and the only reason we're playing is to keep the fingers happy. I have so much more focused, relaxed energy in my fingers when I'm playing to keep them happy and treating it like a game.
It reminds me a little of something I read in one of Barbara Sher's books (I think it was "I Could Do Anything if I Only Knew What it Was, which I mostly skimmed): if you don't like your job, make it into a job that you do like, and then decide whether you still want it. There's something about fooling yourself into thinking something is fun that either makes it actually fun, or makes you more skilled at it, or sometimes both. When are you just fooling yourself, though?