I think regardless of whether or not I get the MSM fixed up, I plan to try something new soon. Right now I'm debating a couple of options, and I'm interested in hearing some opinions from you guys.
One would be to go with an STS car. The advantage of a Miata would be that I already have a good suspension I can take off the MSM. Otherwise I've been looking into a Civic or CRX for STS.
Another thing I've considered is a C5 corvette (a car I've always wanted) for A/B street.
I think an STS car would be a better way to improve as a driver and have plenty of direct competition locally, but the C5 is an attainable childhood dream car, and V8's are fun.
Feel free to offer opinions on those options, or anything else you think would be fun. Keep in mind the autocross car would be an occasional commuter as well.