Excellent work Paul. Great inspiration to do a Desert Hawk! Have you ever tried any of the "dust" products like MiG pigments? You can brush them on dry or make a thin wash. Another thing I do to represent dust is add a tiny bit of light grey (say two drops) into your final matt/satin finish - test this on some dummy model first. This gives the model a slight dust/fade finish - very subtle. Otherwise the decals are just too bright and vivid. Masters of these filtering techniques are guys like James "Haggis" Haggo and Chris Wauchop. Wauchop is my modelling hero - when it comes to WW2 stuff. I have tried the oil dot technique and think it's brilliant as well.
http://chriswauchop.com/Practice on some old crap model. I have a Trimaster 262 which I have used over the years as my technique "tester".
Man, you are pumping them out - Bravo!
Cheers
Adam