My pool is finishing its 11th season, and has never been closed. I have roughly the same setup you have except mine is 18 x 36. I shock my pool when the water gets to around 60 degrees or so, and then just cut my pump run time to a few hours a day, except during freezing weather. When the air temp is below 30 degrees at night, I run the pump all night to keep the pipes from freezing, and otherwise just maintain the pool normally. This has worked well for me, but then we only get a handful of below-freezing temps during the winter, and it's almost never below freezing for the whole day. I think last winter it only went below freezing a couple of times, and never got below about 22 degrees.
The only problem I can think of that you might run into would be a prolonged freeze where the temps were below freezing more more than a couple of days, coupled with a power outage that would prevent you from running the pump. That situation would be a disaster. So...you'll have to make the decision as to what's best for the climate in your area, but in that worst case scenario, I have a generator that I could use to power my pump if I needed to--and that particular situation is very, very rare down here.
I must say, it's nice to be able to look at a pretty, blue pool during the winter and to be able to jump in as soon as the water temp is warm enough!!
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