Rode clips and straps for years and swore by them, but only 'cause I hadn't tried anything else or thought about it.
A middle aged man on an old mountain bike needs to take his plates off the pedal and put 'em on the floor, or wave them around, quite a lot. Straps or SPDs inhibit this natural and pleasurable activity.
What do clips/spds add? A certain pedalling efficiency? Sure: but compared to the inefficiency of the average retro bike/rider, it's a drop in the ocean. Plus, the small efficiency gained from clipped-in pedalling is easily outweighed by the larger disadvantage of not being able to put your paws down when you need to (rocky terrain; riding in a slow convoy at a retromeet when the dude in front has a mechanical -- it can happen; stopping to admire the view; having a whizz; trying to do cool foot-down broadies in the dust -- why mountain bikes were invented!).
Plus, SPD shoes are crap. Yes they are; heavy, stupid and unnecessary (do you have special driving shoes? When you go to the over forties disco, do you take your special dancing shoes?)
And anyway, why would you need the small efficient advantage that spds allow? To win a race by a few seconds? Pah! Only about three people on here do that anymore.
No my friends, clipped-in pedalling is wonky and pointless. Get some nice light flats, a pair of light shoes and rejoice. You will quite literally become closer to your environment; you will feel an inner glow of pride; passersby will wonder at your poise and elegance; you will lose weight.
Amen.