Frankly if your paid-tier is so underwhelming that people would 'bunk off' and keep renewing free trials then I think your offering sucks.

Look at current Flickr, trying to force users into a one-size Pro membership. They're not listening to light users who won't pay $50 + taxes + currency conversion fees to get 'stats and partner offers'. Instead people are creating multuple accounts and storing 999 photos in each, for free. Flickr should be in that space with $10 Basic accounts