Here are some results from my testing this....
So, I made a quick demo. There are 2 layouts, each with 99 custom movement objects of the same image bounded to the screen by obstacles. Layout 1 has 99 different objects while Layout 2 has 99 instances of the same object.
Draw Calls results:
99 different objects: 5.8% cpu
99 instances of same object: 2% cpu
Now.... when I delete half of the objects on each layout:
50 different objects: 3.8% cpu
50 instances of same object: 2% cpu
So there is quite an overhead for drawing different objects v the same object and a constant and significant minimum overhead on my computer at least for drawing anything on the screen. I didn't have the energy to create different images for each object to see what, if any, that sort of change might make on the draw calls. So, for my laptop at least, although the draw calls demanded 3 x the processing power to draw the different objects, the increase was still only 4% in magnitude - not a problem for most desktop games I am guessing, but such an increase could cause a slow down on a mobile device.