I think Lucid is on to something with just about everything he said... I REALLY like the idea of paying for extra plugins, etc. Great way to keep income coming in and interest in the project.
Kinda like the old salesman tactic. Once you get somebody to buy, then you offer them just a little more for a few bucks, and then a little more... and before they know it they have paid double what they would have originally spent. Not that you are trying to trick anybody, but it is a logically way to keep revenue coming for those interested in the project as well as get the baseline money for those that want to just buy it once without nags/ads, etc.
Edit: Second what toralord said...their ideas sound ALOT better than what was orginally proposed.