I am not a pro. I am just an amateur with more money than sense. My current camera is a 60D, although I have a 5Dc I am playing with. What makes me need a new camera. Nothing. I don't need the cameras I have.
What makes me want a new camera is a bit more complicated. I want a new camera when I find the camera I am shooting to be limiting in some way, and an alternative exists. The first new camera I wanted since acquiring my 60D was a 6D, primarily for its jpg ISO 6400+ IQ. While I can shoot my 60D in good light with decent results at 3200 that is as far as I like to go. ISO 6400 is iffy; fine in decent light, not so fine as the light deteriorates.
The second new camera I wanted is the 70D, primarily for its AI-Servo AF. The 60D has respectable AI-Servo performance. My grandson is getting older, more mobile and faster. Couple that with my decreasing contentment with the 60D's AI-Servo performance and now I want a 70D, too. Still debating.
Just the rambling thoughts of a photoholic with more time and money than sense and talent.
Dedicated APS-c shooter. Gripped 60D, 60 2.8, 10-22, 15-85, Σ70-200 OS and a big white something or other! Plus a 5D w/28-75.