Room acoustics

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

My secret methodology for treating room anomalies. You need to find and map out all the sound pressure peaks in the room, incluing the 3 dimension space of the room. The most effective way to do this is using a test tone (s) and SPL meter. I select test tone(s) around 315 Hz or thereabouts since that frequency is very revealing, and effective, but you can use other frequencies, too. This will allow you to find all sound pressure peaks that are say, 6 dB (i.e., 4 times higher!) above the average sound pressure in the room. Generally speaking, these peaks will be found in room corners, at first reflection points and on the wall between the speakers, on the wall behind the listener but also at random and unexpected locations around the room, including in the 3D SPACE of the room. Sometimes right where the listening chair is located! 😧 All of those peaks 6 dB or higher act as "speakers" that interfere with the primary sound produced by the speakers. The objective is to reduce those peaks as much as possible - without producing side effects. But trying to treat the room by ear is a fool’s errand. It’s like trying to solve n simultaneous equations in n + x unknowns. Sure, you can do better than nothing but you will only find a local maximum, not the real maximum.

There are a great number of devices that can be employed to defeat the peaks once you’ve located them. I can vouch for Traps, Hemlholtz resonators, tiny little bowl acoustic resonators, crystals, Mpingo discs, Room Tunes Echo Tunes, Golden Sound’s Acoustic Discs, Skyline diffuser, but not (rpt not) SONEX.

This may be the moment to introduce the so-called Schroeder frequency, named after the German physicist Manfred Schroeder. The Schroeder frequency denotes the crossover frequency between the chaotic behaviour of sound waves above it and the discreetly spaced peaks and dips/nulls below it. Above the Schroeder frequency sound waves bounce around the room, producing many small spikes that are closely packed along the frequency range. Below the Schroeder frequency the peaks occur at the resonant frequency of the room's dimensions, and create big peaks at particular frequencies and again at their upper harmonics. These so-called room modes are large and pretty far apart, so they are quite obvious to the listener, with a boomy bass that often lingers on at particular frequencies. See here for more explanation: https://www.soundandvision.com/content/schroeder-frequency-show-and-tell-part-1
The Schroeder frequency can be calculated approximately, and depends on a room's dimensions. The larger the room, the lower the Schroeder frequency, from about 200 Hz in smallish rooms down to about 100 Hz for a large room. See here for a calculator: http://www.mh-audio.nl/sg.asp
Knowing the Schroeder frequency of your room is important, because treatment above it has to be quite different from treatment below it. See here for more discussion: http://www.linkwitzlab.com/rooms.htm
To put it simply, treating the frequencies above the Schroeder frequency is a matter of adding damping material like rugs, bookcases etc. It can often be achieved without too much intrusion into the style of your home decor, although there are also more visually imposing solutions from the world of studio design. The exception to the idea that dealing with these higher frequencies would be quite easy is if like me you prefer a modern minimalist interior. Such rooms have a hard acoustic and softening the acoustic without changing the style of the interior is a challenge.
Conversely, adding rugs and the like to reduce peaks below the Schroeder frequency is pointless. What you are dealing with here is big resonant peaks that can be tamed in only three ways. The first is so-called bass traps. Unfortunately at the frequencies we are talking about these bass traps are necessarily large and ugly. The second is multiple subwoofers. Main speakers have to be located for best mid range response and imaging, and that is not necessarily best for bass reponse. So separating bass response from the main speakers allows you to locate the bass speakers at the best spot for them. Traditionally HT subwoofers were used alone, but it is now increasingly understood that using multiples smoothens their response because their response peaks and dips do not coincide. See here for some explanation: http://www.acousticfrontiers.com/20101029using-multiple-subwoofers-to-improve-bass-the-welti-devanti... You get twice as many peaks, but of much smaller amplitude, and that sounds a lot better. To be sure, this is still not an argument in favour of stereo subs. It remains true that at these low frequencies sound is not directional, so dual subs are mostly still connected as mono subs for a somewhat smoother response compared  to stereo subs.
Finally, remaining peaks may be equalized by dsp eq units like the Antimode 8033 for subwoofers. The results can be quite stunning with a far tighter and more tuneful bass. The limitation of room eq is that it works best in only one listening position. The smaller the room and the higher the frequency that has to be equalized, the more localized the good result. Using two or more subwoofers gives a good result over a much larger listening area than with a single sub.
It should also be obvious that a larger listening room is highly beneficial. Its Schroeder frequency will be much lower. And the lower the room mode frequency, the less obtrusive it feels. Moreover, equalizing a lower fequency works over a much larger listening area than equalizing a higher frequency.
So, to be honest, good bass reproduction in a small listening room of, say, 10x14 feet is not really feasible. There is no space for bass traps, room modes are at too high frequencies (and their upper harmonics even more so), and equalizing them only works for a very small listening position. In my view, the simplest solution for small rooms is to just use little monitor speakers without too much bass output. The brain is pretty good at imagining there is bass when there really isn't much of it.