When I bought my bike, I thought that if I ever started racing, I'd buy something fancier. Fate had other plans and I don't think that the difference between one 26"-wheeled aluminum hardtail frame and another is very significant. So I'm focusing on getting my current bike to work for me as well as possible. I think that the most important attributes of a bike when trying for maximum performance are fit and that everything works.
My teammate gave me a kickass deal on those shifters several weeks ago, and since my chain and cassette were both pretty dead anyway I figured I'd take the opportunity to upgrade. The stem is something I won at a race in February and it gives me a little more aggressive position. I'm planning to try an even longer stem when I get my current vehicular drama sorted out.
This crankset is the gift crank for my birthday. It's got a little larger big ring, a little narrower stance, and the middle ring is made out of steel and carbon fiber. Totally cool.
And this is the bike in its curent configuration. A new stem could be a near-future item, since they're available in a bin for $10 each at one of my local shops. I'd also like to put on new brakes, with larger brake pads and a choice of compound, because the current brakes don't always survive the whole length of a muddy race. Also, the brakes I'd like are self-adjusting. After that, a new wheelset would drop a ton of weight and help the rear tire sit a little better. Beyond that, I don't see the utility of putting on a nicer rear derailleur unless I wear out the current one so the bike would be maintenance-only.