Great write up! Some additional things I've wished were there:
1) The ability to easily convert photos/videos uploaded at full resolution to the High Quality, free size.
2) The ability to easily "upgrade" photos that were previously uploaded using Google+'s free resolution to the new High Quality resolution (by re-uploading).
3) Allow searching by any metadata associated with photos/videos
4) Expose all the search terms that are available: for example, searching by camera is possible by searching "#CameraName", but this is not explained anywhere, and there's no way to see a list of the camera names that currently exist in the database.