I am going with the idea that this system is for HT first and music second:
The 500 is better than either the 3200 or the 12nsd, IMO. The 12-NSD is better than the 3200 at least for HT. The 12-nsd has a bit of a bump in FR at 50-60hz and it hits quite hard because of it. It makes music a little unnatural, at least to me. I think the Paradigm 3400 is more on par with the 12-nsd only smoother and the 500 would be that much stronger than either one IMO. Only you can decide if it is really worth the extra money.
Having said that I think you would be very happy with any of the subs you have mentioned. Have you considered the EP350 from Axiom? I think the EP350 is Axiom's best deal, it is a great sub and does very well with either music or movies, nearly the equal to the EP500, again IMO.