If you're intent on upgrading, I'd go for the brakes then. Does your bike have cantilievers? If so, any decent V-brake set will give you superior performance and much easier maintenance. You needn't spring for the XT brakes, though. The "Straight push" feature of the XT's is considered by many to be overly complex and unnecessary. I can't tell any difference between XT and LX as far as braking force is concerned, or a decent set of Avids either, for that matter.
No need to replace hubs and such unless you just want to see those stickers....