Before you got the dumbphone were you a heavy user of email and calendar information? I wonder if I'd miss things like that if I went back to one. I cut the cord with cable so I don't see why I couldn't go back to a dumbphone.
Calendar info can be synced with nearly all phones in other ways.
If you don't recieve important calls all that often, test yourself. Leave your smartphone at home for a week.
If you don't use it much while you're out and about, could you not simply have forgone it, planned your trip 5 minutes before you left home, and checked your email that evening?
I also don't like planning or sticking to plans when going out (how much fun is that anyway?). But I do like to get information on the go, for whatever I decide to do.