It's indeed questionable how much, if anything, you save by going up the technology curve with water heaters. As I stated in another post, every time I look at this, it does not appear worth it to me to get a more advanced, energy efficient water heater, eg power vent, tankless, etc.
In the other post I gave numbers for two GE 40 gal water heaters at HD. One a typical basic water heater, the other a higher efficiency power vent. It was about $500 more upfront cost for the more efficient one. Using DOE numbers, it would take 14 years to recover the extra upfront cost. And that doesn't factor in the time value of money. Taking that into account, you'd likely never recover the money. It also doesn't take into account that the std water heater uses a chimney, the power vent is a direct vent type and it also requires AC. So, if you're going from regular to power vent, the install cost difference could add hundreds more to the price. Then instead of 14 years, it could take 20+ years to get your money back. Well beyond the expected life of the unit.