Well, for one thing, you and I probably like about the same ride handling compromise, IIRC, the MSM is ~300lbs heavier than my 99 base model car which, will make a significant difference.
If you want to dial out some body roll, I think you can do it with upsized sway bars. There should be tons of info in the forums at miata.net on that. There have been many attempts (with varying degrees of success) to turn the MSM into a great autocross car. Apparently, depending on your local venue, the 6 speed can be a bit of a problem (having to go into and out of, 3rd gear occasionally).
Of course, FM or Goodman Racing will take you as serious as you dare to go!
You really do start loosing some of the 'streetability' and it's hard to go back ;-)
Chris
99BBB