Aurick, thank you very much for your reply. Based on your input, I was able to find a solution without having to break up the model. All this is probably not an issue anymore with ZB3, but just in case:
I created a polygroup of the item I needed to size large enough to be able to do detail work on. I hid the rest of the model, and set the center pivot point on that portion. Then, using tool->deformations->size, I increased the size of the section that I wanted to get close to, and decreased the size of the rest of the model. Setting the pivot point causes the portion that you’re reducing in size to size towards the center of the section you want to edit.
The net effect is that the part you don’t want to edit is shrunk and moved to the center of the part that you do want to edit, and you can zoom in closer because the shrunk part isn’t hitting the border when you zoom.
EDIT: Uhoh. I’ve just noticed that the reduction/reenlargement of the part you don’t want to edit has a strange pixelating effect on the surface of the model. 