I just bought my used 2006 GT a few weeks ago with only 22K miles on it. I've driven a number of two-seater convertibles, mostly Honda del Sols and one Toyota MR2 Spyder. The Miata definitely feels like more car -- the leather seats seem solid and luxurious, and I love the dashboard layout, redundant layout controls, remote entry, carpeting and cloth top. The trunk is practical, although not as large as the del Sol's. The only real drawback so far has been the gas mileage. My del Sol averaged 32-33 mpg in mostly city driving; first two fill-ups with the Miata have shown 24.9 and 25.9 (the second with about 50% freeway driving). That's in line with published figures, but is still not great.
Lower the seats a bit, since my head hits the closed soft top; install real roll bars (it appears the roll bars are for show only -- I think they're made of plastic); improve gas mileage and/or make engines use regular unleaded gas instead of the recommended premium.