After years and years of toeclips, I finally made the change to SPDs.
Somewhere I have leather shoes with cleats for the toeclips... what a pain to walk in those.

I don't find the SPDs to be perfect for walking. Fine for errands, but I like to change shoes if I'm planning on wearing them for a few hours off the bike, or perhaps heading out to do outside work. The soles are hard, and more slippery than other shoes, but presumably wear less too (only 1/8" or so and one wears below the cleat). But they are far more comfortable (and safer for walking in) than my old Italian road shoes.

As far as foot retention, (toeclips or SPDs (or others)), I personally like it. I've been riding a bike with the toeclips for so long that I feel very uncomfortable without it. But, I can certainly ride a bike, at least for short distances without it.

I don't know what my average crank stroke is like. I do know that I pull up from time to time, especially when accelerating, climbing a hill, or pulling a heavy load. And, I get a better short-term power boost from the cleats. Once clipped in, I never have to worry about where the feet are.

Good or bad, I wonder if the clips/cleats give better calf muscle exercise, as many people ride with a mid-foot position with flats.

Anyway, I agree that it isn't a one-size-fits-all thing. Cleats are good for some people. Not necessary for others. I don't see a lot of them around town, but when I did the DRT race, almost everyone had them.