Well, if you're not driving on rough roads then I'd lower the car a bit. I found that on the stock suspension they tend to feel a bit like the tail is floating. Nice quiet tires, new weather stripping around the windows and targa for less wind noise and replacing the old noise dampening material with newer, lighter and more effective sound insulation makes a huge difference on those long, casual cruises. A well dialed in alignment and new wheel bearing often makes a huge difference in comfort as well.
CUP HOLDERS!!! Add cup holders! I never understood why the Supra's (and MR-2's for that matter) never came with cup holders... GT my hind end!
Oh, and a good sound system NEVER hurts.
A piggyback setup which allows you run a bit leaner at cruise is very nice... I can't think of anything else at the moment... Okay, yes I can, new foam in the seats.