I owned a 6-speed Miata SE with the Torsen limited slip for about 2.5 years. It was the second generation Miata (2003) so fuel economy wasn't great, like 22mpg if you do exclusively short trips, although 30+ on long highway drives. I like convertibles and Miatas are funny with resale; if you take good care of them, the resale is excellent. I purchased mine for $10,500 and sold it 2.5 years later with another 10,000 miles on it for $9000 cash.
They're not fast cars, but I think they fit Mustachian principles pretty well if you're looking in the used market where the majority of the resale hit has already been taken. I wouldn't mind having one again, although clearly I can fit a ton more stuff in my compact hatchback/wagon than I can in a Miata. OTOH, I have family members close by with a variety of cars including a compact SUV, so I could see myself using my bike & trailer for the short trips, car for the medium and fun trips, then borrowing the SUV for utility trips.