I happened to try NXT over MP just this past week on a Laguna blue Miata . . . I applied NXT with a PC, which left a thin coat that wiped off easily after about a half hour; no apparent problems with application or removal. However, although the car looked awesome under artificial lighting and in the shade, pulling it into the sun revealed fine, oily smearing that would not wipe off (wiping just seemed to push the smears around, rather than removing them). With so much talk of NXT working over glazes, I thought I'd give it a try, but apparently whatever MP leaves behind is too much for the light cleaners in NXT to cut through.
I re-did the car the following evening using Glanz Wax. Again, the car looked awesome in the light in the shop, and in the artificial lighting in the parking lot. Unfortunately, the sun had already gone down, and I haven't heard back from the owner to see if there were any similar problems with the Glanz Wax.
I have used MP followed by GW on my own silver WRX, though, with good results.
Tort