I agree with those that say that they should just insert a small acoustic set somewhere in the flow of the main set (e.g. mid set) and not strictly as an "opening" set. And they should experiment and diversify ("throw caution to the wind!"
as Dave said when he lauched into "Fool to Think" or was it "Raven" for the first time acoustically solo at Benaroya Hall.. they need to have that attitude more.. and throw caution to the wind. So acoustic and electric integrated into one main DMB set. first they perform a quiet one, then a loud one, then a quiet one, a loud one, and then something in between.. LOL.
I am not against full acoustic sets for one night in a two or three night venue however you can't assume all attendees are attending both nights. I would say only a small minority attends multiple nights (< 5%).. and I would hate to miss out on acoustic or electric songs by picking the wrong night.
Last - I want them to bring back opening acts other than themselves. it was a great way to get acquainted with some bands i would have never heard otherwise. And it should lend itself to some interesting collaborations possibly.. where either Dave sits in with the opening act or vice versa..