I live with high-mineral water too, from a well. Probably not the same chemistry as yours, but here are some thoughts.

As far as cleaners go ...

By using Comet etc. you've probably created extra surface area, with all the micro scratches, that make the buildup more tenacious than ever. I wonder if buffing or refinishing is possible? Car wax (crazy idea)?

CLR works, but you have to rinse it after.

Vinegar works too, though more slowly. Look for higher concentrations: pickling vinegar is 7% (as opposed to the standard 5%) and works a lot better; and some granola-greenie-eco-stores sell stuff that's 50%, which is strong enough to eat through paint or eyeballs, I guess.