al74dart,
I'm with MetroMPG on this
- if the dirt bothers you that much, you have to take the hit and add the deflector
I'm sure you can find a bolt out there that someone says helps with dust
depending on the driving you do there may be ways to mitigate the issue by removing it on high speed highway driving - because there is less dirt
you could attempt side skirts and aft wheel fairings to lessen the dirt you kick up
Or... If you have a high pain threshold you could develop your own spoiler like this:
Green Car Congress: Novel Spoiler Design Reduces Fuel Consumption for Minivans, SUVs
but with out a wind tunnel (or tremendous patience) this would be hard
but if all you want is the dust gone - buy a big scooping spoiler
it is the simplest path to clean(er)