Since they are that old, it wouldn’t be difficult to check the combustion chambers. Go here to see how to do that: http://www.waterheaterrescue.com/pages/WHRpages/English/Longevity/water-heater-maintenance.html .
You can take pictures and post them here and I’ll tell you if I think they are goners or not. If not, you could replace the sacrificial anodes and keep on going.
The main “benefit” that you’ll get with replacement is vastly increased complexity, a need for a kind of maintenance you don’t do now, and general annoyance. My own is now 35 years old and there is nothing attractive to me in the new generation except that some of them have better insulation.
You can find my thoughts about Tankless here: http://www.waterheaterrescue.com/pages/WHRpages/English/Longevity/tankless-water-heaters.html
Tell us more about that final point about the 150 percent. Where did you see that? Electric or gas? What Btu or wattage? What is the exact wording they use?