Well, as a member of the SCA for (ahem) baout thirty years, I can say that it is at it's best when somebody's thoughts tun something like this: Hey, that's interesting! How'd they do that? I bet I/we could do it...let's give it a try.
I like the SCA because it does not focus on military history, so as a woman, I am not limited to cross-dressing or just being a camp follower. If I want to dress up funny and cook over a fire, I can do that without paying for the privilege. It also covers about a thousand years, so there's a lot to play with. Since I am needle-impared, my clothing is either purchased, or not all that great, but that is not held against me.
Admittedly, I am not that active, but I go to the Pennsic War (probably their largest event) to see friends, to shop for stuff I couldn't get anywhere else (at least not easily), and for the classes. I've tried out everything from Mongolian cooking to cracking a bullwhip. Not everything in the SCA is the quintessence of academic research, but a lot can be, and it's nice to sample a bit of something without having to spend hundreds to satisfy your curiosity.

I've been to a couple of renfaires, but I didn't find much to do there besides eat, see a couple of decent demonstrations and shows (falconry, plays, etc), and look at a lot of vendors' booths. Pretty, but a bit expensive for me. (remember, speaking just for myself here.)