About a month ago, I had a 20 minutes (alone) test drive in the RX8 and the MX5 back to back. I preferred the MX5 of the two. The RX is a good machine, but I would have taken the MX5 over it.
I had a similar experience. As many of you here who have been around the forum for a while remember, I frequently bucked the trend and played devil's advocate, speaking up against the RX8 as perhaps an overpriced alternative to the better-equipped RSX Type-S. Then, finally, I decided I should actually drive one.

WoW!!! As others have said, the numbers on paper do not do justice to the pure driving enjoyment of this car. It's plenty quick and when you rev it up (as it LOVES to do), it sounds glorious and really hustles. The steering / handling is extraordinary -- and is the key reason why I think if it were my decision to make, I'd choose an RX8 over a 350Z and save myself some bucks along the way.
When it came right down to putting my money where my mouth is, I drove past the Acura dealership and drove the RX8 back-to-back against the MX5. My short-list consisted of these two machines and a used 330i w/ sport pkg. When the Bimmer reminded me of why I got rid of my old one (electrical gremlins on the test drive!), the decision came down to simply which one could be a better value. I negotiated both at the same time and when the dust settled, for me, the better value (ie. cheaper fuel, maintenance and insurance costs in addition to lower monthly pmts for the same amount of fun) steered me toward the 2-seater. If I had a little one, it'd be a different story.
In 3 years' time when the MX5 is about to be turned in -- if the market remains as is (which of course it won't) -- the RX8 would be top of my list for replacements since I expect to have a youngin' on the way by then.
Mazda certainly gets my

for giving enthusiasts the luxury of choice... RX8, MX5 and MS6... delicious variety there!