If you're looking for simplicity I'd suggest you'd be better off simply running the cold water through the coil first and then into the hot water tank without a loop. That would be the absolute simplest method.
That would be the simplest way, but the water would always be stagnant until something called for hot water. Wouldn't the water just boil to the point where it wanted to exploded or melt the pipe? It would seem that a pressure relief valve would always be letting off steam or allowing water to pour right out of it.
The relief valve is higher but I just wonder how fast the water would actually circulate. WOuld it dribble out of would it be a nice siphon.
Trader that's a big concern for me, how would you know if you were getting the most out of that type of setup? It seems that a pump would be the best way to know you are getting the most out of your system.