Wharton, answers to your questions:
"1. Removing all telephone books from the house.
I don't see this, unless the telephone books are blocking the speakers or air vents on the equipment. But, if you are using them for isolation under equipment, or to sit on so you are at proper listening height, keep them."
Telephone books hurt the sound, but not because they are blocking the sound or damping something. It's a mind matter interaction issue. Take all telephone books outside or just throw them away. Who uses telephone books anymore? Easy to test.
"2. Removing all plants and flowers from the listening room.
Plants are good natural acoustic treatments and look nice too. I'd keep them, but you have to be careful not to over water them. Also, watch out for strange infestations of bugs and plant diseases."
Plants and flowers, while attractive, hurt the sound. Mind matter interaction issue. Easy enough to test, no?
"3. Removing all empty beer, etc. bottles from the listening room.
Good idea. Probably more sanitary too. Since I don't drink, not much of an issue for me."
Empty bottles act like Helmholtz resonators, even one bottle on the room is quite noticeable.
"4. Removing unused speakers from the listening room.
Probably the most important suggestion, i think, because those cones move sympathetically. Unfortunately, I have a large home theatre system in the same room as my hi-fi (not connected to each other, electrically or through signal cables), but the extra speakers are there, and it would be a giant pita to move them for hi-fi listening. I do turn the amps on that control them, to 'charge them' so they are less compliant and the speaker cones less prone to sympathetic movement."
All musical instruments including speakers should be removed for best results. It has very little to do with the speakers cones resonating, as can be confirmed listening through headphones. Alas, it's a mind matter interaction issue.
"5. Removing all unused amps and other components and cables from the listening room.
Dunno what this would do - isn't that sorta the old Linn mantra? I have a bunch of equipment for the home theatre system that is rack mounted in an alcove adjacent to the hi-fi, not part of it and those racks aren't going anywhere (they are about 6 feet high and bolted to the floor). I am not looking forward to breaking them down when i move, which- hopefully, will be soon. New dedicated and far less cluttered room to follow in new location."
Removing all unused electronics from the room improves the sound. All unused cables should also be removed. It's a mind matter interaction issue.
"6. Removing all Sonex from the room.
Sonex is an acoustic treatment, right? I haven't heard that brand name or term in a while. Not sure where you are going with this, some treatment, if properly applied, is good, but I'm not sure about Sonex."
Sonex, you know, the one used in many recording studios, degrades the sound, even in small amounts. Same goes for those foam padded chairs from Ikea. Easy to test.
"7. Removing speaker grills.
Could improve things if not acoustically transparent."
Almost all grills are acoustically transparent. Nevertheless removing grills will improve the sound. Another mind matter interaction issue.