I have a 26'x20'x8' room
Listening/viewing position will be a large sectional sofa, about 15' back from the speakers.
I'd like the speakers to sound excellent without having to be in the perfect triangulated position relative to the speakers. My current bookshelf speakers are quite sensitive to this.
Sound I be looking at bipolar main speakers, or is it really just a matter of woofer size and power? Would a good set up bookshelf speakers and a sub really accomplish the same thing as a floorstander for a large room, or would it be more fluid and natural with larger mains to be begin with?? Would I be giving up much of the clarity I crave with bookshelves?
Budget expectations are steadily creeping up...lets say $1200 for floorstanders
As you realize, answers to your questions are complex. Pyrrho has already mentioned some.
Wide sound dispersion, and the resulting sense of a wide stereo image from two speakers, are achieved by several different design approaches. I'll mention some.
In one sense, wide dispersion and speaker size are
inversely related. Large coned speakers may have narrower dispersion than small coned ones. But this depends on the sound wavelength. This is true of all speaker drivers – its a matter of physics.
A cone speaker can make widely dispersed sound if the wavelength of the sound is larger than the diameter of the cone. As sound wavelength gets shorter, and approaches the cone's diameter, the dispersion of the sound begins to get narrower, to the point where the sound beams in a narrow pattern. So dispersion depends on size of the size of the cone
and the wavelength of the sound. Think of a mid woofer in a 2-way speaker. A well designed speaker crossover will take that into account and pick the crossover wavelength at the point where wide dispersion begins to drop. You'd be surprised how many commercially available speakers fail to do that. If done well, it creates a speaker with both wide dispersion and good imaging focus. If done poorly, it creates a narrow sweet listening spot that requires high volume to make the sweet spot get larger.
The reflected sound from the rooms walls also contribute the overall sense of spaciousness. This can vary significantly with room size, reflectiveness of walls, speaker and listener location, etc, as well as wavelengths where this is most affected. It can take a lot of trial and error to optimize this. In your case, a large room may help minimize the effect of room reflections.
With monopole speakers (drivers mounted on the front of a standard cabinet), most sound is directly radiated from the front, but their location in the room, near or far from walls does have an indirect effect.
There are dipole and bipole designs that change this balance. A dipole (imagine a speaker with an open back) radiates sound both forward and rearward, and a bipole has one or more drivers mounted on the front and rear to do this. There are omnidirectional speakers with one or more drivers facing upward or downward rather than forward and backward. These multi-directional speakers often have a different sound, and have different location requirements than monopole speakers. They are an acquired taste that not everyone likes.