For additional data, Wrecking Balls Arena has had about 500+ individual downloads and only 6 "full-game" purchases since the game was released about 2.5 months ago. Currently, I have the price of the full game ($3.99) listed in the game's description on the store so people know how much the full version costs before they download the game, although for a long time it was "for sale for $2.99 until August 28th".

I see the "all games are free-to-play" system as a double-edged sword. On the one hand, there's plenty of awesome games I never would have played/bought if there wasn't the free version to try, but on the other hand it does have the good potential to decrease sales.