Room acoustics

Have fun! 

a couple of tidbits from an Email exchange with ASC (Tube-Traps):

1. ona hardwood floor, put a rug down, which should extend all the way underneath the speakers, sticking out for at least a foot in all directions from under each speaker. The rug should also extend all the way beneath the listening chair. This can have a large effect, softening the perceived hardness and brightness of the sound.

2. for glass windows, use the heaviest-available theater drapes from www.rosebrand.com -- even these are acoustically transparent below 1,000 Hz -- but the main components of stereo image formation occur above 1,000 Hz

I have a basement listening room with low ceilings.. two things I've done that have helped reduce peaks, resonance and echos: suspended ceiling with Armstrong tiles and fully carpeted. I'll check which model of ceiling tiles I have, they weren't cheap but they do a great job of sound absorption in the mid to high frequencies

To answer the original question without having to use in room measurements yes acoustic treatments on side walls for early reflections, in corners and on ceilings for slap echo and also diffusers on back wall do make a huge improvement for reducing brightmpness and increasing imaging and overall clarity. You can hear everything way more clearly and focused just using side wall early reflection absorption. I can tell you from experience in my 12 x 13 basement theatre / listening room it was one of the best improvements to sound and coherency I've done. After treating my room I heard instruments, nuances and background vocals I never heard before, everything sounds just more tightened up, better bass and just much better. 
You ears tell your more than anything. 

Hmm, your ears can tell you a lot, but sometimes there are some specific issues that are audible but not easily remedied. These peaks and nulls, which seem to be persistent once the easy room treatments are done, are so specific in their frequency band, that I think you'd be hard pressed to identify and fix them by ear. At least that's my experience. A little bit of data can be useful.
But your mind is still the ultimate decision maker on sonic performance. So it does have to sound good, whatever it measures