I have both.
VT-50 is brighter than VT-60
*Yes, but in a light controlled or dark room, it's not a significant difference. Both are plenty bright for viewing. Not sure of any difference in a bright room as I would never view these TV's in that environment.
VT-60 has better black level than VT-50
*Yes, on/off contrast on the VT60 is significantly higher than the VT50, and I believe it makes a seat-of-the-pants difference.
VT-60 Motion handle 1080/24FPS is not better than VT-50 or same?
*Look about the same to me. Not sure one is much better than the other.
VT-50 design is better than VT-60
*YES. Other than the stand, the VT50 looks sleeker than the VT60 and looks similar to the ZT60. That clear plastic strip on the bottom just doesn't do it for me. But the low MLL/shadow detail more than makes up for it.
VT-50 is quieter than VT-60 Fan noise
*Mine seem to be the opposite. VT50 seems louder, but perhaps because I have it about 2 1/2 feet from the back wall and my VT60 is about 10 feet from the back wall. When I used to have the VT50 where the VT60 is now, I never heard the fans. Now, I do at low volume, but they are still VERY quiet. Placement does make a bit of a difference, IMO.