I use NXT on my roadster all the time now. I did it over Meguires Gold, which I used over Crystal Guard. Never had a problem putting different things over something else, but I didn't do it the next day. Just when I thought the car needed something again.
We drag race cars over the summer and I try to keep the cars clean at the races and in between. I used to always use Mothers Gold Class because it was so easy, but at the last race we went to in Dallas, I had some extra time and decided to try the NXT on the white vette because it does such a good job at keeping the bugs off the front bumper. They practically just wipe off the XF now, after a few coats of it. I used it on the whole car, but put 2 coats on the rear quarter panel where all the burn-out rubber collects after each run. I would have to use gas or some other harsh chemical to get all the rubber off, but after I used the NXT, I only had to use a dry rag and rub the rubber right off. Hard to believe that such an easy product works so well.
I'd try the NXT next time if I were you. Save that arm. They look a little weird when the muscles of one are bigger than the other, hehe!

Car Looks Great! You're lucky you're in CA where you can drive it year round and have it look so good.