[InvisiBill]

Slightly different, but replacing the way-too-soft fork springs on my 500 made a huge difference. I still consider it the best mod I've done to the bike. I'm a bigger guy and went with .90kg/mm, which is actually still a tad soft for my weight. The NewGen isn't quite as undersprung, so it probably won't be quite as dramatic a change for you (depending on your weight).

The Intiminators also helped perfect the ride. However, they're more expensive, more work, and didn't help as much. I like them and recommend them for anyone looking to upgrade the forks' damping system (I still think they're a technologically superior solution over emulators), but springs should be done first (with priority based on how far off the stockers are from your weight).

I have a Penske I need to install one of these days, but dropping in a NewGen shock was a huge upgrade for me. The spring is 73% stiffer than the 500's stocker, and a much better match for my weight. After installing it, I could feel the rear end moving, but it felt controlled and appropriate. According to RT's calc, it's actually too stiff for many NewGen riders (good for about 215lb). Having experienced an issue with a modded shock that was binding, I can say that a too-stiff rear will rockinghorse and cause the front to do weird things. I doubt a heavy stock spring would be as bad as my binding shock, but if you happen to be tiny, I could see it causing noticeable issues.

Getting the spring rates to match your weight will allow the bike to bounce the proper amount. That makes it easier for the damping system to control that movement. When you've got weak springs, it moves too much and the damping system has to try to constrain all that extra flailing around. Changing the springs doesn't change the damping, but fixing bad spring rates can allow the damping to work better.

If you don't mind paying for an aftermarket shock with the proper spring, that's probably the easiest and best way to go. The GSXR shocks seem to have a variety of spring rates available, so if you want to be cheap (and do some modding) you can probably still find something close to what you need. I haven't seen much (but I haven't looked a ton either) from Kawasaki models that would be comparable. Kaw seems to use similar mounting setups for a lot of their shocks, so there would probably be less work in getting it to match the Ninjette's mounts, if you could find something from a different bike that fit the desired specs.

There seems to be some question over how accurate RT's calculations are for the rear spring rate. Buying a few GSXR shocks/springs might be a cheapish way to try out different spring rates and see what actually works well for you, as opposed to buying an aftermarket shock and multiple springs for it.