The whole Inspector palette system is great.

The ability to do PostScript fills and strokes (and have them live-preview via Display PostScript) in Altsys Virtuoso was flat out _amazing_.

Ages ago, I once used the CMYK adjustment to get a rough preview of a multiple spot ink job à la Cerilica Truism (which you should have the person doing the CMYK stuff look into --- it allowed one to set paper stock colour options and then simulate multiple ink mixes, including spot colours --- also spot types, so there was only a single set of ink mixes, but if a spread had coated paper on one side and uncoated on the other, the appearance matched what one would have had to use two ink swatches for in other apps).

Also, Graphics Find and Replace is invaluable for working on complex files w/ many objects.