Hmmm, the headers may indeed be unnecessary. I installed them when I got the driver just because, well, it was in the instructions. I thought maybe they got used later on in the install process. Not sure.

Quick note (all credits to hawaii for doing this way before I ever did, putting me up to this and answering some of my questions along the way that helped me make sure I was on the right path): You can use scratchbox (remarkably easy to set up inside a Debian virtual machine) to compile the latest Aircrack-NG code (using SVN to get it, which is preinstalled in Scratchbox, if I remember correctly) for the N900. If I ever get the motivation and figure out how, I will see if I can take over maintenance of the current aircrack-ng package in the repositories, and push out the latest versions that way. But until then, the aforementioned is a good way to relatively painlessly get the latest versions of aircrack-ng.