The main reason racers wear clipless pedals is keeping their foot securely attached to the pedal. Imagine sprinting wildly trying to break away from the pack in the last stretch of the race - you want your foot to stay on the pedal. It's not about speed or efficiency. Several studies have shown no improvement in speed or efficiency for pro racers with clipless. I think a few other studies thought there might be a little. It's a topic of great debate, but there's no "huge" improvement like a lot of people think.

I have wider feet, and after years of trying different clipless and shoes, went back to flats, because I couldn't find a way to avoid hotspots, or knee pain, or some sort of foot or leg pain with clipless. Went back to flats and it's not an issue any more.

Most clipless bike shoes will not change size after wearing them. Most manufacturers have a "wide" shoe - at the $150 price point.

These are the cheaper bike pedals that I think are good for riding with flats, VP Components Bike Pedals:
http://www.amazon.com/dp/B006ZH1H7M/...dp_o_pd_nS_ttl

There's nothing inherently "bad" about clipless, if you really want them go ahead, I just personally wish I had avoided all the time I put into trying to make them work, and stuck with good flats in the first place.