Leave your drivetrain components alone. You can spend a lot of money and there's very little you can do that will improve them. That includes changing from a triple to a double; all you get is fewer gears.
Wheels,
Tires,
Pedals,
+1, and add
Brake pads
Saddle (maybe)
Adjust the fit (possibly a different stem, find the best saddle position, etc.)
Shoes, chamois, gloves...
As Lance says, "It's not about the bike".