Because you are asking these questions in the plasma, laser, waterjet section of posts, I assume you are (never a real good thing, to assume) intrested in one of these methods. Because waterjet is done under water, it dosen't generate airborne abrasive. Laser is at this time too expensive for me to play with, so I cannot comment of it. As I see it the most likely situation you are facing is with plasma cutting. You are right on target to be concerned with the airborn trash with plasma cutting. The danger is both in your personal health and the potential damage to your machine. Plasma cutting just puts a LOT of trash in the air. My solution may not fill everyones needs, but the way I handled it was to mount the rack on the "X" axis tooth down, so the airborne dust would not accumulate in it. The "Y" axis design did not allow the tooth down method so I mounted it tooth vertical. Neither mounting methods have given me a problem with trash accumulation. For personal health, I have put a skirt around my table (cuts 48" X 96") and installed a huge fan to pull the smoke and grit down and out. This goes a long way in keeping the dust from accumulating in the racks or my lungs.
I think it may be proper to look at the expected life span of what we are building when we design these machines, as well as the repair- replacement cost of parts as opposed what it will cost to design a "forever" machine. My machine has undergone several changes and upgrades and if I were to have been overly worried about wear prevention I think I may not have been so quick to upgrade the drive system because of cost. I see my machine as a work in progress at all times and if I ever feel that I have created the perfect design and will never want to change it, I will turn my attention to covers at that time.
never set a pace that you can't maintain
Traveler