Are 3D Movies Worth the extra cost?

Today we went over to the local multiplex to see The Green Hornet in 3D.  When we go the bargain matinee we usually pay $8.50 to see a movie.  However, this theater adds $4.50 to see a 3D movie raising the total cost to $13.  In my opinion there were very scenes in this movie that really took advantage of the 3D technology.  Avatar was another story where the director properly used 3D in most of the scenes.  I didn't think that was worth paying $4.50 extra for this special effect.