To me, there's an interesting difference between stereo and ambience..
A split-stack 4x10 or 4x12, when fed [maybe pseudo-]stereo, will perform just nicely more ambient than pure mono, when using certain effects like chorus/flange.
Most other effects really do not need true stereo - live, that is; an album is a different thing.
Pretty much the only concert ever with a fantastic setup was witnessing Pink Floyd mid/late 80's. but that's of course not for the majority of us to reach - and even then, it was more about creating a real good unified ambience for the whole crowd.
I think a good solution for a band would be to have the bass spread it's mono just fine, guitars do either mono of split-stack ambience, drums be what it is (given the real-estate size and natural ambience), keyboards likely stereo, have own mic-up into a mixer arrangement that'll produce the band's own idea of a wanted, useful mono plus stereo feed to suit this or that venue installation.