Do it! I was very fortunate to have the chance to go to Thermal for the 2-day M school. Other folks have written up their experience better than I ever could, so I'll just say it was damn fun! Our group was a range of brand new (e.g. me) to a couple of folks who were serious about getting an SCCA license. I will also say ... us older guys tended to do a better than the youngin's, on average
My one comment would be to try and avoid the summer season if you could - it was well over 100 for both days, and with poor air quality on the 2nd day some of the cars began to overheat. Still, don't let this stop you if you have the chance. I am definitely wanting to go back for the advanced school when I next get the chance.