Just got the rear end panels for my '78 back from the body shop on Monday(taillight panels, license plate lamp housing, license plate bracket), and what a difference it makes!
I refinished the the taillight bezels myself (separate on later S30's), and let the body shop deal with the sueding agent and the rest of the stuff to get the panels looking good. The light fixtures themselves just needed a good washing with soap and water, and the local old-style hardware store had all new stainless fasteners. I doubt I spent more than $200 for everything, and it probably took less than 4 to 6 hours total.
It's just one step in the full restore progress on my car, but it's really remarkable the difference it made in appearance. You could do it without committing to other body work and it would still look better. You wouldn't have to undo it or redo it if you go for a full paint or body restore later, either. It also gives you an excuse to put in new taillight gaskets and stop any exhaust fumes that might have been leaking into the car. And just about any modern finish will be easier to keep clean than the old one.
Anyway, if you've been putting off restoring old panels, don't. It's cheap, it doesn't obligate you to other projects, it doesn't take long, and it makes a huge difference in the appearance of the back of your Z, which is of course the part most seen by others.
Dave