I agree - it's a good investment, properly installed they would last a long time and save you the nuisance of doing this again in five years. There is a thread with alot of discussion on this subject - search: 2" taller , should get it.

Bear in mind that the 240Z is a 30+ year old sports car with a short wheelbase. It's not going to ride like a modern sport sedan, no matter what springs and struts you put in it.

In general, you can expect the stock springs to ride the best. If you can find a set, the Nissan Euro Stage 1 springs ride nicely as well. Either of these spring sets work very nicely with KYBs. I had KYBs in with the stock springs for a while, and now have them with the Euro springs.

Either of these spring choices will need to be cut down to maintain stock ride height when using any gas-charged strut inserts, regardless of brand. And the only non-gas inserts that I am aware of these days are Koni, which are more expensive and will probably ride firmer than the KYBs even on their softest setting. I have cut my euro springs down by 2 coils in back, and 1 3/4 coils in front to maintain a close-to-stock ride height. Stock springs would probably need one coil per spring removed for use with gas struts.