I disagree with the world map idea. I've seen it done but I've never seen it done good. Perhaps instead make the buttons a slight bit bigger on the top for the old folks and hard of sight to have an easier time finding their way through.
For the most part, other than that, I don't see anything bad about it. You've allready got a good review, now it's time to fill it up with paying customers.
Do the non-paying customers get a newsletter from the site?
If so, fill their newsletter with the adverts instead of the main page. Explain to them that a pay account not only entitles whatever it is that that entitles, but the newsletter has no adverts!
To get a few dollars off me you have to nearly beat me senseless, so make sure it's damned worth it to pay for it. Add more benefits for the paying customers!