I bought a used '94 miata in 2002. It had waterspots all over it, and no matter how hard I tried, I couldn't get them off. I washed, waxed, rewashed, waxed again, and nothing.  I tried "cleaner" waxes, and no results.  My neighbor had a 90 BMW, and the paint looked like new.  She recommended I use Liquid Glass.  Now, at first I was kinda sceptical cause it came in the same kind of can that turpentine/paint thinner come in, and it had a warning about containing petroleum distillates.  But once I tried this stuff, WHOA!!! Water spots gone with almost no work.  Just spread it on, waited a bit for it to dry, then buffed it off.  After a few coats over about a month, some guy pointed out that my car had some dents in it.  I wife replied with "What the hell do you expect?  It's a 94"  The dude came back with "You're ******' kidding me!! That paint looks new!"    And it did.  'cept for the little dents.   Then I took a Clay Bar to it, and re-applied the Liquid Glass.  You could set a Buffing cloth on the hood, and it would just slide down the hood on it's own.  
IMO, this was some really good s***!!  It's not available to me now, cause I nobody in Alaska distributes it, and it can't be shipped up here.  So that sucks.  But the only place I ever found it at was Pep Boys.  It's in a gold can with a red corvette stingray on the front.  17.99.  Not cheap, but well worth it.