IMHO it is well worth it to learn to work on your own bicycle. If you can work on the bike it is not a big deal to try different things with fit, gearing, etc.. Plus if you learn to work on your own bikes they will always be in great mechanical condition. At the first sign of a funny noise, missed shift, or strange/loose feeling somewhere you can figure out the problem and fix it. On the other hand I guess some people have no interest (or ability) in mechanical things outside of using them, so to each his/her own.