Just broke down and finally got a CSA...
I'm not much of a poster, but have always used this site as the best D&D 3/D20 resource site out there. So I should have put up some money before now.
My only suggestion, for CSA subscribers, create an annual funding report that shows how much you need to maintain the site for the rest of the year and what has been raised.
I also would chime in on at least biannually (if not quarterly, put the call out for CSA accounts/renewals).
By the numbers you gave us, it would only take 450 $20.00 (annual) accounts to maintain your server space, with some extra cash to continually improve the site. Hell that is what Yahoo charges for full feature email accounts.
Ideally if enough people annually purchased CSAs (don't know how much that would be) I would expect you to start paying yourself/others for some of their time maintaining/improving the website.
This site is too good a resource to see go away anytime soon.
Edit: Gee this is only my eighth post...