While airscapes was correct, he was a bit "spirited", shall we say, but I understand where he was coming from. He was wanting to stop you from creating more work for yourself.
Having worked on a number of projectors, both LCD and DLP, I can tell you that blasting air into the lamp chamber will (with great probability) drive dust INTO the Optical Chamber and onto the optics where it will show. If that were to happen, then you would have to open the projector, open the chamber and clean those parts. Not a fun job.
Now...unless you see any dust on the image itself, there is no need to do anything other than taking a brush or small vacuum to the vents and crevices on the outside of the projector. How often depends on how long it takes to see any buildup on the outside. If you don't see anything, then you're good to go. Any dust you may see on the front of the lens will bother you more than it will the image as anything on the front of the lens is outside of the plane of focus and will not impact the image. Unless, of course, it's really built up so thick as to reduce the image brightness, but I don't think you would have that problem, considering the "clean ship" you run.