mapman, well, you have a certain degree of image density, whether you want it or not. It's a parameter, a function of stereos and varies according to the design of the speakers. I would say that image density is inversely proportional to the image size, with panel, large line source and omni as champs in the latter. Conversely, I assert that resolution is a function of the system's electronics, not speakers alone. I can often make any given genre of speaker on hand outperform any other in terms of resolution. It's not hard to do.
Image density is a particularly beautiful aspect of sound reproduction, and it happens with differing degrees dependent upon the tech used. The most image dense speakers, imo, are classic dynamics, and they also imo have the highest capacity to focus the center image. The most tightly imaging speakers, along with being the most coherent in terms of wave launch are full range. This is why they are so favored in terms of presenting what is considered exceptionally fine resolution of voice and acoustic instrument. Especially when hearing vocals and instruments produced from a point source, the image density, or solidity is an exceptionally pleasing thing! Some people think that if you explode the images, you are hearing more resolution, while others insist that by focusing the images you hear more resolution. It's all manipulation of the wave to give a sense of pleasure, and I see both perspectives have merit depending upon the goals of the listener.
"Location" for omni speakers is far more nebulous than dynamic speakers. There is no clear fixing of the artists in relative location on the soundstage, but they float disembodied in the air. It's not that there is no center image, but that it is so widened as to be cartoonish as any point source instrument or voice. There is a pleasing distortion added through use of two 360 degree drivers, but this does not simulate well the tightness, the focus of especially the center image. To my ears the image is exploded and suspended in an unnatural way, relative to most live performances. That, I believe is one reason why most do not use omni speakers; they bring a lot of distortion to the "picture" in front. It's an intentional distortion, and has some very pleasing effects to it, including the immersive ness, but it's not imo accurate to what would meet the eyes.
You mentioned the 3-D aspect of music as well, an it varies from the close field full range tightly captured soundstage to the, "it's in your head" effect of the headphone. That is another parameter on a spectrum, and in that respect no other speaker than omni has as much of that umbra of sound, short of headphones. But, it is a matter of trade offs in terms of the particular characteristics of the sound. I enjoy the variety of characteristics that each technology brings, and try to accept the enhancements with each as a beautiful form of reproducing music. Others have strong preferences as to what sounds right, and are content only with one expression of it. Thankfully, we have enough types of speakers to accommodate most visions of what is considered reality in stereo.
I laugh about it now; many years ago I was a hard core panel fan to the point that I was trying to convince others that it was the correct wave form. Now, I think that was so stilted. The entire affair of stereos is about manipulation of the wave form and launch, and novelties capture our imaginations. I find it a wonderful, fascinating experience that even after all these years when I sit down to a different genre of speaker, there is an adaptation period, a time of what used to be about a week, but now is more like hours, where the fundamentally different character of the speaker seems "off" due to it's uniqueness. But, with time, the mind adapts, and soon the sound is striking the ears as normal and with emphasis on the strengths of the speaker's capabilities.
With all this critical analysis of omni you might think I have some thing against them. Not not at all; if I did, I wouldn't have paid any attention to the Model F opportunity, or own the King Tower. :)