well, first change the logo at the top of your page, the one that says, "Our Community". That's make the whole site look more legit
Personally, I don't think forums are a great way to make mad cash online. Your regular visitors aren't going to click ads every time they go to a page, they're there for discussion, not making you money. I agree that the paypal donate button is okay, but if your members think you're in this for profit, they're not going to like your site.
Maybe I'm biased, because I'm not into all the grabby web commercialism like some of the world is, but I think a discussion community should be about meeting people and making friends. If you make some money, that's cool too. but it shouldn't be priority #1.