Yes and yes.

 

I just got an 08 Z full suspension installed, and I find it a little too bouncy for me. If I only change the rear springs to the coupes, will it make any difference?

 

Z Springs are shorter and either are the same or firmer spring rates from a stock G so its weird that its bouncy, Shocks out? How many miles you got?

The Unrevised Z Springs have the rear end lower then the front(iirc)
Revised has the Back sitting 1/2 an inch higher. So no reverse rake

 

That is weird that it's bouncy. I'm pretty sure you have the revised springs with it being '08 so....

How many miles are on them? And do you know how hard the previous owner drove them, did they track it or anything?

 

I guess I mean to say it's a lot more firm. The setup as about 18k miles. Will it be ok to go with a z/g combo on z shocks? Will it change anything as far as the ride quality? I'm coming from a 05 sedan with non sport suspension. Maybe I just need to get used to it.

 

Let it settle for a bit. Pretty sure you can still do the G/Z combo with Z shocks/struts. I'd prob go with that setup myself after I see how 370z rays will fit when I get them. And the ride quality with Z suspeniosn in general is close to OEM so it shouldn't change much going coupe springs in the rear.