Doug,
Bill Pentz did an air quality test in my garage a couple of weeks ago, and that is one thing he recommended. I have a similar "garage" set as you, and I work with the door open when possible. I have a Cleavue, but no other filtering system. He said if I could setup a fan in the back that brought fresh air in, and with the garage door open, the airborn dust that the DC didn't pick up would be more likely to be blown out instead of settling on everything only to be stirred up later. I also blow out the shop with an air compressor once a week. While the DC is really good, there is still airborn dust. Using good dust hoods, while being close, don't always pick-up every speck. I'll use all three methods.