The longest day I ever pulled fully loaded was on platforms with toe clips, and a cheap pair of shoes from payless. 164 miles over a(admittedly low)mountain range and a river valley. And about four days riding on each side of that. Its appalling that I was not crippled, but really the only people who would be appalled are marketing execs who want you to believe that you need the latest riding teck, and the riders who blindly believe the marketing execs.
Don't get me wrong, I own plenty of spds and "appropriate" shoes, and feel that if your feet do get sore then you should use a stiffer sole, a larger pedal, whatever helps you personally. But if you can wear thongs and use rattraps for your touring, then no one should tell you that you cant, unless you ask if they know of something different.