Indeed, a big "THANK YOU" is not misplaced.
I've been a site and forum-administrator myself and I know the amount of time and effort that get's into it. It's ok when you enjoy doing it, but sometimes it's difficult to find the necessary time.
IMHO, the greatest advantage of oOple is that it gathers a lot of (positive thinking) people and by doing so, gathers a lot of knowledge.
I don't think a separate section, for subscribers only, is a good idea. The knowledge has to be easy to get to for everybody, after all, that's what made this forum so great (as it does for all popular fora!).
But I certainly wouldn't mind contributing on a voluntary base.
Maybe an idea: there is a very popular Dutch RC-forum:
www.modelbouwforum.nl and there also, the possibility exists to donate a certain amount of money. It is completely voluntary and all you get for this is a special note under your avatar saying "friend of modelbouwforum" and you also get a little special gift.
I think that if you make that little gift be something like a little decal or sticker, specially made for the contributors, mentioning something like "oOple-friend" or "oOple-M8" ... I am certain you might find many people interested in donating and by doing so showing their aprectiation.
I myself would certainly do so!