Your gas heater should perform wonderfully in the situation you are looking for. I don't remember, did anybody run your #s to see how many hours you needed to run to reach desired temps ? Its usually somewhere between 10 and 24 hours for gas heaters.Can I still run my heater on a 70 degree day even if the water is still really cold?
Even in a most expensive case scenerio, if it cost you $100 to have a warm pool on a cold day, taking 7 kids to the movies (if they were open) would cost at least that much. Might as well swim. And like you said, your sanity is priceless.