Having nothing in your queue doesn't stop you from earning Space Coins. The queue is simply there to help you keep an eye on the progress to your desired game.
(Note: Viewing the Queue can sometimes lower Space Coin production a little - this is a bug we are working to fix)
Did you know?
Adding a game to your queue does not mean it will be automatically purchased.
Once you obtain sufficient Space Coin you will be asked to confirm the exchange.