i hope no one minds if i point to another renderer here... but it is something completely different than maxwell .. so :
not free but for 450 bucks you can get
AIRplayed with the trial a while ago... the plugin interface is oldskool, but it gets most things done. (caustics are not accessible though, you have to script, or add lights in airspace)
and it seems to have a good baking solution.
this is also renderman.. a little bit of a different world.. but together with maxwell you can make very interesting images...
air's rib supports native nurbs curve rendering with linetype support from rhino!!
i think the best solution for rendering curves in rhino i have yet seen.