It only generates about 15k a year in ad revenue. It's fairly low revenue because:
1. Users are spread around the world. This isn't a site with 70% US visitors.
2. The majority of users run ad block, and this continues to rise.
3. Ad rates plummet each year. I earn about 5x less on the site now, than in the past, with the same number of active users, and 3x as many advertisements.
I've tried all the major advertising networks. I setup header bidding and signed direct deals with large networks, such as AppNexus, Amazon, Yahoo, AOL, etc. At the end of the day, ads do not pay well for my audience.
Users can pay $3/mo to remove advertising. Yes, I'm aware that's $36/yr, when the average registered user is generating less than $0.50/yr in ad revenue. About 30% of paying users choose to pay higher than $3/mo for no additional benefit (they can pay any amount they wish). I also have some individuals that have paid thousands of dollars.
What would happen if I offered a $1/yr plan for an ad free experience, so it's more inline with ad revenues? I honestly don't know, but I would guess I would lose a few of the $3/mo paying users, and gain less than 100 users paying $1/yr, so it would likely be net negative.