Not much can be done with the driver seat, short of using some crack filler and leather paint. I intend to do this, just haven’t been quite that ambitious yet.
I’ve replaced all three (!!) shifter boots, both the rubber ones, and the pleather one, all of which were torn. I shampooed the carpets, cleaned the used car lot shiny gunk off the dash, and took the doors apart to lubricate the window mechanisms with some Mercedes Gleitpaste.
It responded well to a good cleaning, though. I stole an idea from a guy on Jalopnik who had an FD RX-7. He took out some of his ratty looking black plastic trim, and polished it. I did this to my shifter surround, and intend to do it to the bezel around the radio and the HVAC too. This is a lousy iPhone picture taken in the dark, but it looks nearly like the “piano black” trim you see on some NC Miatas.