I had issues with hard water spots in my Opti-Coating, and I tried all of the above - thorough washing, distilled white vinegar, a rubbing compound, and nothing worked.
Then, the website that I purchase all of my car-care products from came out with a product called "Spotless" that is specifically designed for the removal of hard water spots -
http://www.carpro-us.com/auto-wash/s...remover-500ml/
Since nothing else that was recommended to me worked, and because the product wasn't that expensive, I bought it and much to my surprise it worked. I was just using it yesterday to get a few water spots out, although some water spots might take two or three applications before they are removed completely.
It's very easy to use - you just shake the bottle, spray the area, and use a very soft MF towel to sort of rub and gently massage the product into the area for 30 - 60s, then rinse it off with water.
Normally I don't like to promote specific products because to each their own - especially when it comes to detailing, but I can empathize with your plight in that I felt awful that my car (which was only a few months old at the time) would seemingly have these glaring water spots for the rest of the time that I owned her, and this worked for me.
If you do end up giving it a try I hope it works out for you, and I wish you GL with getting them out regardless of whether or not you end up trying Spotless or take another route with trying to remove them.