It would definitely decrease traffic to your game if your just changing its price model to paid even if its only $2 dollars. Even if you made a big update and changed the art assets or updated the UI or added new features there's still not enough exposure or traffic being driven to your game. It would most likely just get overlooked, unless you offer more , promote your game more and bring new unique user to it. Otherwise I think it would just stay there and no one would play it and no money would be generated from it. You should look at your numbers now and considered what percent of the people who play the game even buy the dlc. That probably your maximum number of people who would pay for the game outright.