adjustable height rear subframe bushings
 

spl has some for the Z32 and i assume they will have some on the market for us some time in the future. they state it raises the rear roll center but increases anti squat.

my questions are, would it be a good idea for our cars to increase anti squat any more than what we already have? would a raised bushing increase anti squat on our cars? is it a good idea to raise the rear roll center without raising the front, and what does that do to the roll couple? what other things would be affected by doing this?

Roll couple is independent of roll center. Its a measure how much effective spring stiffness or wheel rate you have at either end of the car. And if you look at setups made for the platform, it can very pretty wildly from neutral to the you must be joking level.

SPL's bushings are not doing a wholesale redesign of the suspension or all the other bushings in the system. What they are talking about are suttle changes vs truely adding or deleting oem anti dive or anti squat elements. Which will still have their own cause and effect on what happens when you apply traditional or by the book tuning practices on the car.

I can think of other things I would replace or buy wel before this product would come onto my radar.

From SPL's web site.

Our subframe bushings also allow the subfram position to be "raised" up to 1/2", which will compinsate foll center for a lowered cat at the expense of incrased anto-squate. our slike-in shim system allows you to quickly raise or lower the subframe to fine tune the roll center/anto-squat behavior to your preference- a new avenue for suspension tuning

If you're asking these questions then you need to do some more modeling and testing. This kind of mod, as mentioned above, is a fine tuning thing and would be a solution to a problem posed by a specific race track or driver preference.