Support a premium site?? Sure, sign me up!!
How much to charge?? Hmmmmmmmmmmm-I know another TGM site charges about $40/yr.---and I signed up for that, if that gives you a clue. Not sure what the "break point" is for the average person who views this site on a regular basis. Perhaps you could develop your ideas for the premium site, post those, and then take a poll as to what people would be willing to pay. Yearly access fee vs 6 mo access vs 3 month access, prices for each, etc. Random thoughts after being up for 18 1/2 hrs.
Bottom line---if you build it, they will come. Dr Dave