Replays on of course, you can limit the gain of coins, so you discourage the grinding or major exploitation of the coin system, however leave the high score record the new replay if higher , also if is higher instead of the normal coin reward give 5% of it... so for instance you award 100 coins per normal level give a 1-25 coins reward based on how big is the difference on replay if the player did a high score, if he didn't beat his own old high-score before he replayed give him 1 coin.
always reward players, no matter if they lose or not, rewarding them makes them feel a bit better, then just losing stuff and or playing without a purpose even though in the cases where they lose (die etc ) you give them rep points, little time bonus exp to regain its lost exp etc etc etc...
just make sure you dont stop rewarding people will make ur games much funnier to play and worth playing them.
giving people in game rewards its not like your selling them a real thing... your real thing is ads... or the .99 cents fee... the options in your game are free ... you have to think of it... as a very complex package u want to sell and resell or give it for free that can be reused all the time... dont think like you sell carrots in market place... where u add ur loses on planting, the transportation and taxes for uncle Sam... thats no fun.