I agree with what Karl says about SM. I'd add that while those in the middle are the ones you have to watch for, I still don't think SM is nearly as "bumper car" as many try to make it out to be. I've done a lot of racing and been close to a lot of people, but just really haven't had a lot of contact. I've seen a lot of people do stupid things that could have caused contact, but you learn pretty quick how to spot those guys, too.
I'd add that *most* people in SM seem to care about the SARRC type sprint races. IMHO, those races are won and lost by getting in the top three or so of qualifying. If you can't do that, you can't win. At least not at VIR full, where there is too much talent and the gap gets too large on lap one to ever make it up in a short amount of laps. But CCPS and ECRs are where things get much more fun, particularly since a good many of the SARRC hot shoes are scared to run the longer races for fear of hurting something, or they just want to get on the road home quicker. Personally I usually run SARRC races, but it's my warm up for the ECR and/or CCPS.
That said, don't think you can always race every class available every weekend. I like to think I'm in pretty good physical shape in general, but the heat in those cars can be brutal, even with cooling gear. I thought I could do a double SARRC and then CCPS and ECR at CMP on Memorial Day this year (they spread it all over three days). What I didn't realize was the ECR was 2:05 and was on the same day as the CCPS (okay, I knew it, but what that *meant* didn't fully occur to me for some reason). So I ran the test day on Friday (four 20 minute sessions...I had to skip the last one to attend a graduation), then all the SARRC practice and qualifying and races (I think it was 20 minute practice, 15 qualifying, 30 race, and that was both Saturday and Sunday), then ran part of one practice on Monday to get some rubber buildup off tires. At this point, I was feeling pretty well worn out, and it was Monday morning and I had only run one session that day (and I took the toter to the track so I could get maximum rest by not having to drive to Camden for a stinking hotel), and not even all of that session (five laps?). I then ran three laps of the CCPS qualifying and quit (got a flyer in and didn't need to do any more...the Toyos were overheating just enough that you weren't going to go faster if you got a good one in early anyway). Then did three laps of the ECR qualifying. Then started the CCPS race. Damned engine started overheating about 15 minutes into the 45 minute race. I pulled it off track and it turned out it was the water pump. My rental crew (OPM) would have been happy to throw another one on for the ECR, but at this point I said no way. I would have killed someone or myself trying to run a two hour race that day. I packed up and went home.
Most people are probably better at realizing their limitations than me.

At the very least I should have skipped Sunday entirely if I was going to try to do all of Monday, but in reality given how hot it was down there (gates of hell comes to mind) I don't think it was realistic to do both races in the same day. I'm sure a few brave souls did it, but I doubt many folks who ran all weekend did it.
But it is very nice that there are a lot of options for SM at the regional level race weekends to get seat time. That Memorial Day weekend was still one of my best weekends at the track as far as qualifying and finishes. I've always liked the track, but now I'm starting to get into the good time ballpark.
Given the price of fuel now, I think you can actually road race regionally for about the same price as doing national autocrosses, particularly if you're autocrossing something with large (ie. more expensive) tires.
--Donnie