From my experience, and I've switched a lot of players positions, if a guy is losing WE a position change will usually give him a big boost. RB to TE makes for a really fast TE. The one that I like best though is QB to K. I have recruited to do this, but usually it's just a walk-on. True story, I won a conference championship game because my opponent's BAD walk-on QB came in and turned the ball over multiple times. If only he had banished that walk-on to the bench as a K.