For everyone else- the Mazdaspeed Miata is NOT the new body thats out now, its like my body style.

As far as bang for the buck, not going to beat a MSM. You can get one with less then 10,000 mi for well under 20g...and that means the car is still under warranty. Try finding a good S2K with most of the warranty remaining for under 20k.

There are no known issues with the MSMs. You can scour any of the miata forums and look for problems, but there aren't really any. A couple people have had to replace betterys..under warranty. But no recalls or tsb's on the engine/drive train/suspension. With little work to a MSM, it'll be very fast. Liek Ran said, replacing the intake and adding a exhaust and mbc, the cars will make well over 200rwhp... which should be more then enough, anything more and i suggest some aggressive drivers classes. To me, the MSM isnt as snappy as the S2K when making sudden turns ad on the limit driving.

We can't assume the person is question is going to be racing the car or just enjoying it as a DD. Also, the seating position in the S2K is kinda odd... the top of the doors feel too high and impede view. The Miata has a smaller blind spot. Miata has manual top with GLASS window... much easier to maintain.

When it comes to mods and prices, MSM wins again.
Intake (includes MBC) - $300
Downpipe and exhaust- $900 (for the best of the best)
Springs (stock MSM shocks are VERY nice Bilstiens) - $180
Roll bar - $400

There are a few other misc. mods that are no more then a couple hundred dollars that are good. With those parts, you're at ~220-230 rwhp and still getting 30mpg.

The S2K is nice.. if you get a newer one and have a lot to spend on parts.