The key word being significantly impacting the shape though. I was under the impression you don't want to change anything about the shape. Like if I delete the loops in the middle, the inner circle would have corner edges instead of the smooth ones.
or instead of deleting the support edges and stuff, i like to make my blockout, shape kinda medium poly, and copy it twice, on one copy i add support loops and subdivide, and the other copy i optimize the best i can. or just do your highpoly and use retopo tools, to build a new mesh around it.
Nurbs? No, you wanna use subdivs. Meaning just model a low poly and put turbosmooth on top. That way when you remove the turbosmooth, you still have a lowpoly cage there. You could also just take the turbosmooth down to subdiv1 instead of removing it altogether. That should be pretty close to the original, and you'd just…