Its not like a mono guitar going thru a mono effect to a mono looper to a mono amp?
I stopped trying to loop a stereo signal along time ago, I actually didn't mind that after closing the loop its sounds different.
I have a stereo signal in my effect chain, ending in reverb (an effect that just doesn't really even work in mono, apart from the sometimes cool "mush" sound. I take a mono send to the loopers, and then each looper has a "stereo-izing" effect. so everything SOUNDS stereo, just not real, proper stereo.
I dont agree that there is a "sweet spot" where you will get the correct sound, well there is, but there ALWAYS is... and a "proper gig" its somewhere just in front of the front of house sound board., and in a live band, you can can easily be stuck on the side of the room with the bass amp... and a stereo delay will just be a bit more on beatish or off beatish, depending on where you stand... and thats just great!