I haven't been to San Miguel de Allende in years but when I was there it was a very tame quiet town. It's very touristy and there are lots of expats, which is not necessarily a bad thing. I'm pretty sure they are there for good reason, it's gorgeous. The locals are friendly and the light is incredible there!
I would bring whatever camera you want and take lots and lots of pictures. You're biggest risk of theft is probably a hippie backpacker!