There are a lot of things that go into making a great sounding room. Some are more important than others. Some are huge, other smaller "Nth degree" things. And sometimes, two different approaches solve similar acoustic problems to varying degrees.
For example, speakers with uniform directivity are able to mitigate many of the problems of room acoustics. So some speakers will sound better in a bad room than other speakers will in a good room. Of course, the best thing is to have great main speakers with uniform directivity and multiple subwoofers in a well damped room. But that's not always possible. So sometimes, you have to work with what you've got.
Anyway, foams and fibrous damping materials work pretty well at damping higher frequencies. They can't solve room modes, but they can help with things like ceiling slap.
I agree that there are speakers that sound much better than others in the same room. It is interesting to read all aspects regarding insulation and I think it is one of those topics that's non-exhaustive.