The stereo or mono debate will never fall short of differing opinions. I've run stereo guitar for decades with a good measure of success, however I'm the only guitar in the band and my stereo sounds are not dramatic left and right type stuff. I'm using stereo as more of a "thickening agent" than anything else. Multiple stereo guitar signals is more of a challenge to mix and balance while keeping a reasonably consistent sound throughout the venue, but certainly not impossible by any stretch. At the very least, from a sound tech perspective, I would NEVER want a pre-mixed signal coming to me at FOH. I'd rather deal with 4 guitars, all running in stereo, where I have control over all 8 channels, then to have two of anything sent to me pre-mixed. What sounds good in your monitors or IEM's is likely not going to translate to a good mix out front. As a sound tech, I'd say you worry about the stage, let me worry about FOH.