Dsper,
Listen to Maplegrovemusic.
Unlike a couple of posters on this thread who lack first-hand experience in their own room with treatments (Elizabeth and Rrog, correct me if I am wrong about that, but you previously have acknowledged that with your silence), you will find hundreds of posts by people with actual experience in their own rooms talking about the dramatic improvement room treatments can make. It is not voodoo; it can be explained by physics. It is hard to believe what a huge difference it can make until you actually experience it.
As far as the best place to start to maximize impact, I would agree with Maplegrovemusic that it is absorption/bass traps. One thing to be careful about on the absorption is that for it to be "broad band" (that is, effective for a broad range of the frequency spectrum), it generally needs to be at least 4 inches thick. This can the DIY corner traps (sometimes called super chunks) that Maple speaks of. The GIK Tri-Traps are a reasonably price version of these that are pre-built. GIK (I am not affiliated, just a happy customer) also has absorption panels that are broad band, such as the 244 panel. While thinner absorption panels may have their uses in certain spots, ONLY using the thinner ones can result in a room with uneven frequency response because the lower frequencies are not being dealt with.
The main difference in room treatments with Maggies is how to approach the wall behind the speakers. Most people prefer diffusion for the back wave, but others prefer absorption. In my experimenting, I found that both diffusion and absorption sounds better than a bare wall, but that diffusion sounds the best and keeps that big, live Maggie sound. I actually have a combination and have GIK tri-traps on the floor below the diffusion, which really enhances the bass. It is surprising to find out you were not hearing certain notes that you can now hear after the room treatment. Also, I completely agree with Maple that when the bass is improved, it also improves the mids and highs.
Good luck!
