That sounds like a very lively room! As to the specific question, I can attest that too much treatment can degrade the sound. I moved my system into an untreated room with absolutely nothing on any wall or window. It was like an echo chamber in there. I purchased a room treatment kit from Auralex and went to work. The kit included more treatment pieces than my room required, as I had some DIY panels, but that didn't stop me from using them.
I would listen as I went along and it did get to a point where I was noticing a degradation in the sound from too much absorption. I removed some treatment until I got it correct, or what I thought sounded best. Some of what I removed was behind the speakers. A totally dead wall does sound like overkill to me but your ears will judge. Good luck and do post your system. I'd be interested to see the outcome.
I would listen as I went along and it did get to a point where I was noticing a degradation in the sound from too much absorption. I removed some treatment until I got it correct, or what I thought sounded best. Some of what I removed was behind the speakers. A totally dead wall does sound like overkill to me but your ears will judge. Good luck and do post your system. I'd be interested to see the outcome.