Considering how many spammers we have, it's obvious the captcha and evil fee doesn't stop them. Since the Merit system now makes account farming pointless, would it be worth to try running the forum without evil fees for a while?
The evil fees are designed to stop the serious spammers, not necessarily the sig spammers who are trying to make a few dollars making low-effort posts. The spammers the evil fee is designed to protect against are those who advertise services, spam links unrelated to the topic with the hope they will be seen by google when they index the forum, and other useless posts. These spammers typically use automation, so without the evil fee, there would be nothing to stop them from scaling their spam using an unlimited number of accounts. The spammers do not need their posts to remain on the forum for very long, usually only long enough for search engines to see their posts, and if they make enough posts, the search engines will eventually index a thread when the post is still up.
There might be an argument to say that the evil fees are too high, and we should consider lowering them. I don't see any reason why someone should need to pay $20 or $30 to have the ability to post, and this is far above an amount that will deter the above described spammers.