You have some valid points that people complain about all the time and most,if not all cruise lines basically ignore their own rules regarding saving seats, etc.
With regards to making announcements regarding same in the show lounge, they do make announcements several times and also remind people several times to not take video nor use cameras as the flash could cause one of the performers to possibly be momentarily blinded and fall, etc, but people ignore that request too.
On a recent cruise a couple sat next to us in the main show lounge--the lady was next to me-- and she immediately started taking flash photos. It blinded me every tiime she took one and after several minutes I asked her to please stop, that I wanted to see something of the show too and she was blinding me every time she took a photo. They didn't like it but did quit.
Bottom line, I think you mean well but you're very unlikely to get anything changed regarding seat saving , etc. with the cruise lines. People have complained for years and it hasn't stopped yet.