How did you apply the mild abrasive polish?
By hand, or machine?
If you applied the mild abrasive polish by hand, you might try using either a dual action polisher or a rotary buffer if you have access to them. Its surprising what a machine can do with the same products over what your hand can accomplish.
This same type of thing happened to a Corvette owner over on CorvetteForum,
http://forums.corvetteforum.com/zerothread?id=788320
I invited him to bring his Corvette to the San Diego Corvette Detail Day at Meguiar's this last weekend, which he did.
I became to busy to capture the water spots in the clear coat finish with my camera, but the rear of the car definitely had round water ring spots evenly distributed throughout the finish, on the top, sides and back.
We took some DACP with W-8006 on the PC on about the 5.0 setting to it and this combination removed the water spots.
It did take some effort and some time to remove them and he the owner actually still needs to go back over the car to remove them all, but he now knows how the right combination of products, together with time and pressure will tackle the problem.
Newer Corvette clear coats in my opinion are incredibly hard, his finish had multiple coats of a competitors product on it, but whatever was in the mud puddle water etched right through it and stained the finish.
Just goes to show, there is only so much protection something you pour out of of a bottle, or scoop out of a wax can offer against chemical attack.
Here's a picture of the owner working on his car,
Here is a picture of the results in full sun,
I can tell you for certain, we could not have removed these etchings
in the paint by hand, at least not effectively.
If you can get your hands on a machine, try removing them again, you might have better luck.
Mike