The pair valve removal was am improvement for my bike. I did it at the same time as the flapper valve removal. I lost the flat spot in the lower midrange and my bike ran a little cooler.
Advice of what not to do... the cam silencing gears. Not one bit of a performance help and you have to listen to a bike that sounds as if it could blow up at any given moment.
As for brakes - do you have after market lines and pads? If not, please ride one that does. It will be your next purchase, they do get that much better.
Aftermarket Suspension is not necessary for riding, but like the brakes, when you ride one that has it, you will see the difference and throw money at it.
Do the "soft rev mod" also. Big help for track riding. Those extra couple hundred RPMs can help you get around some bad shift points at VIR.
Another free-ish mod. If you want the bike to turn in better, you can put a shim/spacer (read: big ass washer) between the top mount braket and the frame. Your bike will look funny sitting on the kick stand, but it will definately help with turn it. I also run a 180/55 tire when I reun street tiers. I run a 190/55 when I run race tires. I do not advocate the use of a 190/50 unless you only ride in straight lines.