It sure would be nice if you could set the dpi of each individual viewport rather than the whole sheet layer. I haven't check it but wouldn't setting the an individual viewport dpi high rather the whole sheet layer make for a smaller final VW file? We do a lot of combining rendered viewports in openGL, others in wire frame, and others in hidden line on a single sheet.
Wanted to add in here. We had a project that went from 260MB to 1.7GB. It took us a whole morning to figure out the problem. Turns out the culprit was a high resolution site image taken from the client that we added into the title block. The image in the title block was only 1" x 1" in the end, but the actual pixel count was still at the original size. This size then got repeated on each of the 100 sheet layers, adding the extra gig and a half size to the file. A mistake we will not make again...