I don't know where most of the hidden Mickeys are posted currently, but I would put two sets out. One that could be seen when walking around the park, and a separate set (maybe in a different color) that could only be seen from within the rides.
I think it would be awesome if on the JC dock they had rope as one of the 50th mickeys. They also could put a really small one on an eye patch of a pirate or skull and give it a little 50th and crossbones look to it.
My favourite so far is the one on small world because you actually have to look for it.
As for where i'd put one........ no idea. I think there almost everywhere. I would probably have made them less obvious ,although for the average day-tripper they want to be able to spot them all so they cant be too hidden.
I would put a hidden 50 in the toy room in Peter Pan as well as on Dumbos hot on the red band... I would also put one in the snow on the matterhorn... and in the center of the steering wheel on a doxen autopia cars...