Finally unlocked the last character which basically doubles the coins received.
I am at level 47 now. This is a really addictive game, but once I unlock the remaining characters (skipped unlocking them as they don't add much value) there will be no incentive to keep playing.
I also noticed that current level's missions change every time you turn off the game and go back. For example I had to get 2000 coins in one run. next time I opened the game the amount changed to 3000 coins and then 2500.
This happens even with completed missions. I collected 200 gems and when amount changed to 250 the mission was no longer ticked as completed.
Anyway, great game. I would be interested if devs had any plans to add anything to it. Considering that it went free not too long after initial release, the chances for further updates are slim.