I'd try the Rain-X Deep Clean stuff or whatever it's called, and beyond what you've already tried and what's been already mentioned, I'd be out of ideas and annoyed!
This stuff gets the same kind of water spots off my shower door. Its technically for smooth ceran top stoves but knocks out water spots pretty good. Get it at Lowes, Home Depot, etc... where ovens and stuff are sold. You have to rub it on pretty vigorous and let it dry to a haze. Probably don't get it on the paint.
This was the case with my 1995 Defender. Drove me crazy after I polished the rest of the truck.
I used Duragloss NG glass water spot remover in conjunction with a dual action orbital polisher using an orange abrasive pad. Even so, it took a fair amount of polishing to get the glass to be spot free.
get a mobile pressure wash company to wash it with a two step wash. if he doesnt know what that is go to the next wash company. They use hydroflouric acid as the first step which will take that etching off. I was a wash mobile wash guy for a few years.
Please delete and not read if you aren't willing to document this process or carry it out in fulfillment. It may take several days. Just as it took years to get this way (probably) it may take days and weeks or more to correct. So DO NOT expect showroom results in minutes or a few hours. If you will go for it, then proceed.......