I've used scratchX on paint, but not on vinyl windows. Works ok on paint. Best Meguires paint wax is the gold class 3 stage system IMHO. Lots of work, but results are worth the effort! I also like the Meguires NXT wax. By itself it works great too - but not quite the same results as the Gold class stuff, and NXT works best on darker colors.
Not too sure i'd wax the windows though. Clean soft cloth, and mild soap (no windex, or dishwashing soap) for the plastic windows... AND DON'T PARK UNDER TREES!