This is in interesting topic but I doesn't really prove much of anything. It always brings out the great amount of homophobia on Texags.
I think it would be interesting to look at a gay themed publication and see what cars are advertised. We'd see what the carmakers think gay people are interested in. I don't have ready access to those - but I bet the vehicles would be relatively upscale and high quality brands. The gay buyer supposedly has a higher average income and tends to be a careful shopper.
As for Miatas - I do not think they are gay at all. Many here have already pointed out how widely the car is raced and it probably has more racing and performance parts available than anything except American iron.
Read this interesting data at JD Power:
http://www.jdpower.com/autos/mazda/miata/2007 Most of the buyers are male, not female. Read the rest of the article and it doesn't look like it fits a typical gay demographic.
Note too that the MX-5 is widely tested and rated highly by all the car mags - I doubt those are widely read by gay readers.