Hello; A couple of things come to mind. First is the location of the tank(s). If in a portion of the house that you do not normally heat for your own comfort like a garage or basement, then any insulation should help.
If in a part of the house where you live, then the heat that radiates from the tank(s) will become a part of the ambient room temperature. This may be a a more expensive type of heat depending on the effeciency of the house heat compared to the electric resistance heat from most tank heaters.
If the issue is that the heaters in use will not maintain the desired temp of the tank(s), then any insulation should help. As stated a fairly tight or insulated top cover will be a benefit as well.
No way of knowing if it will be worth it to you. When I had some tanks in a basement, I enclosed the area around the tanks and found this to be a help. I simply hung tarps from the floor joists around the tanks and made a door way with some light blankets. I could feel a noteably warmer temp inside the enclosed area.
