Haven't done Natty's over NXT but I did do s100 over NXT 'cause NXT needs something to top it, and I loved the look.
I found NXT would stop beading in 2 - 3 weeks & I was using NXT car wash so I think NXT is more of a polymer polish/sealant and a good carnauba like Natty's , s100, or LS will complete the job.