The best Miata race shop in the Mid West, maybe the country, is here in Indy. Look up Shane at AIM Tuning. All he does is work on Miatas and he's the best around. Their number is 381-0898. I've watched him do corner weighting and alignments. He's extremely good at set up.
I'd recommend the Koni sleeves and threaded perches to go with the Koni shocks. They fit substantially better than anything else and are fairly inexpensive. If you're going with off the shelf Koni shocks, I'd recommend 550/350 spring rates to start and a RB Tubular FSB.
90 Miata - STS #90/190
If it aint broke, don't fix it.