As a former Miata owner, I know that when it comes to car enthusiasts, Miata enthusiasts are, well, extremely enthusiastic. If you're looking for some great information on interior/exterior car care, stereos, tire treatments, taking care of that plastic window, etc. you'll find a wealth of information here:
http://forum.miata.net/vb/
They have a great forum, have been around along time and have well diversified sub-forums to help you find the kind of info you're looking for. It can be a great resource for finding non-Boxster specific info.