Stright off - I loved the dream/premonition Phoebe had, and the Sandman just standing there "this is not a dream". I thought the guy who plays him was great too.
I loved the Sandman's sly little smile when Piper is worried about her dream being found out :D
Sooo the tracer demon took 4-5 bags of dream dust to kill the Sandman and collect all of one bag... that's a loss and is not worth it.
I have to agree with people below though. The tracer knows that if he kills the corporeal dream the person dies with it. So when the sisters are out, why wait just go in and kill the dream states. A pregnant whitelighter can't stop you much.