Ask HN: Converting Mobile App to Paid Version

Recently I've been building up a free android game called Cubes. The initial result has been pretty positive with about 60k total downloads in the first 2 months. I decided to put ads in the app, but have been pretty disappointed with gains so far.

Because of this, I'm going to make a paid version of the game, with a price point of 99 cents. Removing the ads is obvious, and I also planned on integrating with Open Feint (a social gaming framework that provides high score and achievement support). My question is, how else can I make the paid version compelling?

I should mention that users already have the ability to create their own levels using a very flexible xml schema and the ability to select between two "ships". What else could I offer, considering the fact that I'm only going to charge 99 cents?

Search for "Cubes" by "The Mob" on the android market.

Custom level tutorial at http://themobsoftware.com/?page_id=2