Miata - I do all my mods over the winter since summer is AutoX season and I need it running as much as it can be.
This past winter I installed Koni's and a big front sway bar. This winter I might be changing it from stock class to STS2 and if I end up doing that I will be installing coilovers, new wheels (15X7 or 15x7.5), new rear strut mounts (more suspension travel on a lowered car. New end links front and rear, header, intake, exhaust, new bushings. If I end up going that route it will be about $2,000 for everything I need or about $3,000 for everything I want.
MSP - thinking about stealing the adjustable struts and maybe the smaller front sway bar off my GF's car to set the MSP up for AutoX. Need to get some better (lighter) wheels with some real racing tires. Maybe the Kosei K1-TS with some 235/40/17 RA-1's. The RA-1's rub a bit with the stock wheels but I think the 5mm difference in offset with the K1-TS's might get them to stop rubbing. Or I might go for a different long lasting tire from hoosier or avon.
Wheels - $199 each from tirerack.
Tires - RA-1's $172 each from tireswap, Hoosier R3S04 $213 each from tirerack, Avon Tech R $177 each from tirerack.
struts and front swaybar - free and she will never know