I want to get a small compressor to run nail guns, blow off equipment, and
possibly use a HVLP to spray some finishes. I've been looking at the
smaller 4g units, especially the DeWalt D55155 and the Ingersoll Rand Twin
stack DD2T2. Anyone have any experiece with either of these? Both seem
to
be pretty heavy duty (oiled, cast iron tanks, etc) as far as ~$300
compressors go. Any ideas either way?

Nice units, but a bit on the light side for spraying. Check the compressor
duty cycles, you'll be running them flat out with most guns. Many of the
HVLP guns use a lot of air, and will tax a compressor with twice the
capacity. If you don't already have a gun, homesteadfinishing.com has some
nice low cfm spray guns.