Hello, I’d like to back up a bit and see first if your present heater was ever able to give you the hot water you want. If it did, than you don’t need anything with more energy input or bigger storage. Usually, the biggest use in a house is the shower. Have you considered a low flow showerhead, like 1.5 gallons per minute? That change could allow you to go with a smaller water heater. The one case for going with a bigger tank is if you decide to install a heat pump unit. Those reheat slowly, so a bigger tank helps. Also, they may come with incentives to cut the installation costs. Check at http://www.dsireusa.org to see what rebates you might get.
About the booster function, it seems that means both elements can come on at the same time. To me this means you’ll need a bigger breaker in your electrical panel and bigger wire running to the heater. Those might cost something!
One last thought is that you test for a cross connection. If the plumbing is leaking cold into the hot side, you could imagine the water heater is to blame when really it’s the plumbing. You can find guidance in “tanklets” for how to do that test. 😎