Advancing the timing is a way to eek out a little more efficiency. The problem is when you set it too far forward. Instead of pinging like a gas engine (well, it always pings but it would ping more) you would have a head gasket job in the near future.
One of the great things about a diesel engine is that you can run many many more alternative fuels than with a gas engine. A gas engine can run any fuel that readily vaporizes. A diesel engine can run any fuel that is somewhat lubricative and is not too thick to pump. IE, ATF, veggy, WMO, bio... you get the point. (see signature). Just, as you will read most places talking about it, filtration is the most important part. You could set up a simple series filter system or just jury rig one up to try the oil you get from your next oil change. With your arsenal of cars, you could cut your fuel usage quite dramatically just from oil changes
However, the one thing I have noticed is that my diesel does NOT like to be operated cold, then shut down before getting warm. If I make a run that is that short, I take a gasser.