to add my personal experience with clipless vs non.
I started using spd back in the early 90s, and I found even back then, that I could climb hills often one gear higher with the spd shoes on vs platforms. That sold me on them, and yes, shoe stiffness is a factor too, but riding a few of my bikes with platform pedals sometimes always shows up how my spd has an advantage, and coming from a touring perspective, I'll take any percentage more , it adds up over a day.
plus Im not a strong strong rider, so I'll take what I can get.
but hey, you prefer platforms, thats cool. It aint a contest .