Here's my 2 cents:
First let me say that I don't question the expertise of Shane. I'm sure he can find great domains on a daily basis.
That said, I don't think it's possible to list 250 "good" domains per day (depends of course what you define under "good"). 40-50 would be more doable, I think. I guess time will tell if it's possible (should Shane decide to launch this project).
Anyways, gettting a daily list of "only" 50 good domains per day for $20/month would be worth it imo. But not if there's 249 other subscribers seeing the same private list. The more people sign up, the less valuable a list like this becomes for the subscribers and the more valuable it becomes for the creator. The trick is finding the right balance. Otherwise it's doomed to fail.
People need to be realistic as well. A lot of the good domains in the list will probably be domains you would have found yourself. If a lack of time is the reason to join a list like this then sure, $20 is a great deal. Time is money after all.