I live about 2 hours from Foxwoods and Mohegan Sun in CT. Mailings from each have varied greatly here and there over my years in the area. Obviously as my betting average and visit frequency went up, I got more of them and less as I became more inactive.
Comps vary a lot, and the more networking you do with different hosts the better they will serve you. The $15-40 average bet range you get $5-10 coupons and maybe a small tournament invite of somesort if you show up really frequently. $50-75 range starts getting better comps, including access to the lower level private lounges, some good invites will come in the mail but generally only for weekdays. $100-150 range starts seeing some more elite types of invites like cash giveaway parties, preference in even getting a room at the place on busy weekend, etc. $200-300 average range with 1-2 visits a month is pretty solid gold at that point - all the high level private lounges, all kinds of great parties, shows, nicer rooms if you want to spend the points, etc.
Overall, I was happy with a lot of the experiences I had at these casinos. Obviously casinos in Vegas or even AC can stretch your comp value further since there's more competition. It's best to try out a variety of places and find your niche.