Maybe you dont have to strip it since you are putting the same thing on. I'm not sure. And those cleaners might work too, as well as some glass polishes (I use Duragloss Nu-Glass). Good luck
According to their website, once it's applied it can be reapplied as needed. If you're worried, as the previous poster said you should be able to use a mild polish to take it off.
I'm curious as well, it's about time for another Aquapel application and I was also wondering if it's nessesary to strip the old stuff off for a better bond with the glass.