If I were in your shoes, I would leave the activation the way it is now. Then I'd pick a few people who registered and never activated and send them a personal

If I were in your shoes, I would leave the activation the way it is now. Then I'd pick a few people who registered and never activated and send them a personal email asking if they had difficulties activating their account or if they decided they weren't interested in the system. If you decide to do this, be cautious in your phrasing or you may not get a response. You may get some good feedback from doing it though - and then you'll be able to make a fact-based decision instead of a bunch of guessing.