I don't know if I would go as far as saying the Klasse twins are *better* than GW+PS. I would definitely say that it is another route to take, but not better. AIO is a great product, one of my favorites but Sonus Paintwork Cleanser can pretty much do the same thing, which I believe you already have.
I, personally, don't care for SG on anything but wheels. It's just plain too hard to work with. According to the guys from Einszett, GW is supposed to have the same life span as SG except with a deeper, richer, gloss since it contains carnauba. IMHO, I don't think anything tops Souveran on black, hands down, especially over a good sealant like GW. I'm not saying SG doesn't look excellent, it does. I just find it too hard to work with and since I like the look of GW better and it's easier to use, it gets my vote.
As far as using ScratchX. If you think you have a scratch that PP isn't going to get out, I would recommend using ScratchX on it before PP, that way PP can remove any marring the ScratchX left behind and smooth it out a bit.