Strangely enough - I was asking the same question about my 2005 FZ6. I did the corbin seat and I think it was a great upgrade. Much more comortable and a better riding "feel". No numbness either. The spring upgrades were:
Corbin seat, Galfer brake lines, racetech cartridge emulators with higher weight springs (.85), superbrace fork brace and amsoil synthetic enigine oil.
Summary - the bike performes better in all categories, I am 155lbs and like a pretty stiff front end ( I had a second trip to the dealer for more preload).
The Superbrace is a fantastic investment ($139). I have much more confidence in a hard braking corner.
250 miles so far and I am very glad to have made these purchases. Would love the Scorpion but I think it is too loud for my style. Getting old:rockon: