Yeah I have thought about the rehearsal swing quite a bit. When I use the 'this is just a practice swing' mind trick on myself I get the same smooth feeling swing that I used to often get when I was using clear key. Of course that was until I got into the anxiety mode with clear key that we have discussed in the past. I also get similar results from the 'Inner Game' trick of humming the same note throughout the swing. I don't think that many of or possibly any of those swings were as 'good' as my practice swing though. All of this is fascinating stuff really.
Have you video'd your rehearsal swing vs. your ball swing while on clear key by any chance? I would think that the more alike they are the better you are doing.