you can use bevel on a NURBS?
the only time i've seen NURBS used it to block out shapes because they are much faster to work with than polygons as they are infinately smooth

i'd just convert that to polygons (change the options so you get as few polygons as possible) bevel the edges, then smooth everything
you'll be able to make the exact same shape as what you have with the same number of faces as you have on that
(if it wasn't for your boolean operation or the curve inside, i would have thought this was already made of polygons because everything is so straight)