To #1, this is at best 1-2% of your total power transfer(on the return upwards stroke, in fact most elite athletes don't "pull" up as was shown recently) The real power gains come from riders being able to keep a high cadence even with a horrible pedal stoke technique - which would severely cripple them if they had to use platforms.

To #2 this isn't true, in fact if you repeat the same motion over and over in exactly the same location you will wear a rut out in the cartilage, this spells trouble for doing other things besides cycling. Runners often get the same trouble, it is called runner's knee.

To #3 More confidence because you fit in, one of the best downhill riders in the world doesn't need clipless shoes, and if he can somehow stay connected to the pedals rocketing down grades that steep and over boulders i'm sure you can too. So #3 is the big one, if you want to be a cyclist shave your legs and use clipless... otherwise the fancy boys will call you fred.

From a 17yr old bmx rider, because people will want some numbers...