Think of it this way --
If you really clean, decontaminate, claybar, and run some compound on your top - just as you would do on the rest of the vehicle, you will be getting a lot or hopefully all of the still embedded dirt out of the paint..
I do this all the time - I correct the paintwork and find brown junk on my foam pad that is not the color of the paint or the compound I am using..
Unless your top paint is so horrendously scratched and messed up, you are not going to remove a whole lot of clearcoat anyway, so dont worry about this..
Now that your top is really cleaned, corrected, and very glossy, it is the perfect time to Opti-Coat it and you will never have to do anymore to it again !
It will be totally protected, have an extra layer of product on it that will not come off for a long time - years - and you are totally set !
And it goes without saying that if you do this to the rest of the Cayenne, it will be the only one around that looks that good, and again, the protection will make it so much easier to clean, and you will not have to do much more to it - ever - if you are careful how you wash it so you dont scratch it, and even then, this product is pretty resistant to scratching..
Good luck with this !
Dan F