I have used clipless pedals since 1992 and while people should use what they want, here are my preferences for clipless
-I still feel that there is a certain percentage of advantage using them, specifically when climbing, so I will always take any advantage I can get, especially over a long day riding with a heavy bike. I'm not a strong rider, so like the other guy, I'll take it whatever it is.
-using other muscles is nice just for a change even when on the flats, I like to change up my pedal stroke once in a while and clipless allows this easier imo.
-as I have clipless on the two bikes I ride, its nice to be able to hop stuff and be more secure over rough stuff when going fast (not really a touring thing, but the bikes are used mostly unloaded or commuting)
-pedal life....this will be completely subjective to the actual pedals, but my 1992 shimano spd clipless are still in use, have never been opened and still spin with hardly any play. I figure I'll use them til they break.

I still say that the shoes are just as important, that they fit you really well, give really good support and are stiff to be most efficient for power transfer and foot comfort.
If you have regular pedals and shoes that are good to your feet, thats great. I just prefer spds for my riding.

*all that said, I could see if you are touring in areas with very rough roads all the time, it could be nice to be able to get off the pedals super fast and or not have a spd cleat slipping on rocks etc if you have to walk a lot pushing your bike, but this sort of touring is usually going to be a minority for most of us here and even then, for me would still be a hard decision considering the positives of clipless for riding that I feel are worth it.