Requiring a donation to join seems strange to me. I like the current set up, you donate if you are able or want to, if you can't, or don't want to, so be it. It may turn off potential members. The current setup, where people join, like what they see, and if they can/want to donate, they have that choice.
The KLOV method is interesting.. but it seems to work. Get a referral from someone you know who is already a member, and it costs nothing, if you don't know somebody, 2 bucks will get you in. But, again, not everyone has the 2 bucks, paypal or knows somebody. When I got interested in pinball, the only pinball guy I knew was the retailer who sold me my first pin.
Or, the captcha for the first 20 posts. Is it annoying? YES. But would it stop me from joining a forum I wanted to give a spin? No!
Having said all that.. I'm still OK with having thicker skin, ignoring and reporting posts, and just living with it.