Just like to throw it in here:
Mudbill and I were working on an Engine Scripts page, however, have been overshadowed by Frictional Games; who have since posted development documentation relating to the helper files and the hps_api files, which serve the basis of most, if not all, code you will be using in your .hps files for your maps.
The functions as found in hps_api can be found here and the remaining for the helpers are found within the same wiki folder as the link, as used in the sidebar. Furthermore,
video tutorials have been made available for us to use and reference if need be.
Personally, I'll start looking back into some of the things already mentioned on the OP now, and will continue updating as needed. Feel free to continue posting suggestions as to what we should include on the wiki, and feel free to continue helping out in any way you can!