I agree that removing your stickers now will ruin your stamps.
I always put the stickers on mine as I like to see exactly what is being stamped and where. It is true that they do not stick as well with the stickers on.
I was having the same problem you are describing one day recently. I cleaned my block and Wow, what a difference. Oils from your skin build up on the block and thus inhibit the cling. It is important to periodically clean the block AND the stamp too. I used and microfiber cloth and buffed and buffed the block. I also used it on the stamp but not to the same degree as the block.
I have heard that it is good to use a grease cutting dish soap to clean the blocks.
I have also heard that using the Aileens tack it over and over will actually cause damage. I haven't done this myself, so I'm not sure on that one, but that is what I've read here in Splitcoast.