Robb,
I am not a big fan of layering. However, it does sound reasonable that a top coat of your favorite wax should give you an added measure of protection. How long it's going to last, really depends on the environmental conditions facing your car this winter.
I have been using NXT Tech Wax about every month or two on my own vehicles, so I am going to just try to get an addition coat of NXT applied right before the extreme cold hits sometime late in December. Sooner if it gets a lot colder earlier.
Since the NXT has worked so well, I really do not intend to top it with anything else. I think the NXT will do just fine for a few months. Especially since the surface of my vehicles now feel so smooth and slippery, since it has been conditioned with NXT so frequently.