Setting your suspension correctly for your weight and riding habits is the best thing you can do for the performance and comfort of your bike. Well, light wheels probably get even more performance, but they're in a completely different price bracket.
Many companies sell fork springs and new valves and/or valve stacks. Some, like Traxxion Dynamics will sell you springs, but for their valves (unless you get their full drop in cartidges for a grand) won't sell you just the valves without them professionally installing them. Some of the ...