Suspension upgrades are the best money spent on a bike. I've never heard anyone say the $$$ upgrading their suspension was not worth it no matter how much they put out. If you push the bake at all, even just street riding you will tell the difference.
My wife bitched about the $1000 I spent on my ZRX shocks until I took her for a ride. Even as a passenger she could tell a big difference.
I've spent about $1500 on the ZX10, peneke rear double clicker and the forks redone with penske internals. Well worth it. You can spend less or more, but spend what you can, you will not be disappointed. Just make sure you use a good suspension company, not the dealer or some hole in the wall.