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.
so far... knock on wood... i haven't even come close to a tank-slapper (on rc). and being in new york, the cracks, tar strips, heaves, pot-holes, are plenty. the one thing i really like is that the front end feels planted, unlike the 929 which always feels like its gonna wash out on me.
Ask Shep if you need a damper and he will tell you that you definitely do need one. Had he had one on his RC51, he may not have went into violent tank slapper and hit a wall sending the bike into a ball of flames.
Personally I think any bike bigger then a 600 needs a damper without a question. I also think that all sport bikes should come stock with one like the gixxers do.