Once your mount is polar aligned, it will stay polar aligned "forever" unless you bumped into the tripod, or the mount was somehow moved by winds or earthquakes or other things.
In short, you just need to polar align once and it will stay aligned!
Guess my original premise was a little unrealistic. I think anyone would be looking to get a little better or a little more capable with every purchase. Unless you were buying for some academic purpose, you would be unlikely to buy more than one mount at a time.