I disagree with the suggestion that a 3rd party pedal would be needed to get a good doubler effect. If you want to play with that, use variable delays. Look for some discussion on this forum about the Dynaflanger, which is basically an envelope controlled delay. These things all sound so distinctive as to border on strange, however.
I mostly disagree with the suggestion to play with haas delays, though you'd have to try it yourself. If you do, listen from a few different parts of the stage and be sure to find those points where you've got weird phase canceling or reinforcement. It might be fun for you, but it doesn't always translate well for other band members or the audience.
I would say the key to "filling out the sound" is to have the right tone in the first place—one that sits well with your band's sound and mix. Then get your guitar in the P.A. and let it be heard properly. This will sound very natural and has worked through the years for thousands of musicians in bands with just one guitarist.
I like your first idea too, of creating two different signal paths with different tones and running them in to two different speakers. Don't rush towards placing the speaker cabs in a wide position however—what you're after is a tone that is sonically broad and dynamic, not necessarily one that is physically separated. Some physical separation is great, but don't overdo it. Speaker height as well as width can be manipulated. Also explore what happens when the different sides have different amounts of distortion, or altogether different effects.
