Because they offer some cheap turbo fun, I've looked into these. I asked about them on here a couple months back and didn't get much.
While I'd love a Miata, in my area my price range seems to only turn up early beat B6 PILES. For what those piles command, I've found MINT Capri XR-2's.
While they don't offer the same virtues as the Miata, I'd be looking at mostly 99% drop top fun and putzing around town and about 1% Miata stuff...
Check out teamcapri.net as it seems to be the only forum for these things. The admin there can tweak the stock ECU to run more boost for a small fee if you send it his way.
I've never owned one, but here are some things I've learned:
-1991 cars suffer from the same crank issues that early B6 Miatas suffer from. It was cleared up for 92-94 cars.
-1994 cars have better suspension parts, but are pretty hard to find
-The aftermarket is scant. As some have mentioned here, some nice suspension upgrades can still be had. There was some overlap with the 323 GT/GTX aftermarket, but most places that offered 323 stuff (like Corksport and Racing Beat etc. haven't for years now.) Aftermarket camshafts from a B6 Miata will bolt in. Kelford apparently makes a nice set in various sizes.
-There is some compatability with other vehicles. The stock IHI VJ14 turbo is related to other Mazda VJ turbo's of the era. Popular in the 1G F2T Probe/MX6 world, the VJ14 can be "hybridized". While keeping the VJ14 hotside, the compressor wheel and housing can be swapped with that from a Probe/MX6 VJ11 or that from a turbo from a 87-88 T-bird turbo coupe. Using the T-bird stuff on the Probes usually gives them a nice boost, so I can only imagine the same for the lighter B6T cars.
-You'd have to dig on Teamcapri, but IIRC the exhaust mani bolt pattern is almost identical to that of a D-series Honda. A cheap way to upgrade to a non-IHI turbo is to slightly modify the flange of an eBay D-series turbo mani.
That's all I can remember right now.
There was a guy on that board with an XR2 that put the B6T top end on a B6 bottom end for higher compression. Then, he somehow fabbed in a DSM 16G, added an FMIC, and I think some fuel mods. The car apparently ran high 12's spinning and torque steering, but was still decent enough for DD duty.