Everything has a law of diminshing return, but true energy efficiency
can not be acheived with out the extra cost. Payback will be evident and
real as I took out a Electric Rheem with a blanket an went fron 30 $ to
6 $. Yes electric is double the cost but my sawings exceded that.

Insulate all pipes of hot water , use closed cell foam the type that
has glue strips installed so taping is not necessary. Doubling
insulation is not a bad idea since 1/3 of gas costs can be heating
water.