I'm at the $10 level, which I think is a fair price (a bargain, even) for the amount of value and entertainment provided by the main podcast and AP podcasts. Having access to After Hours, WoD the Heck, and options to play in online games is a great reward for recurring payments.
I don't really have any suggestions for improvement; the only thing I find a little worthless is the "early access" to APs being only a day ahead. But, some listeners might really like that.
If you do want ideas for additional content, some podcasts on Patreon release mini episodes in between episodes. Maybe record a quick and dirty extended shout out (like, 10-15 minutes or something), without any editing or adding music or whatever, and just drop that to Patreon backers every week (or two weeks).
Just glad the Patreon (and the site!) continue to be a success.