Cinema4D's Attribute Panel allows a user to select multiple layers, and modify various attributes that those layers share, at once. After Effects could certainly benefit from this. Could be extended to shape layer properties, etc.
Say you have three layers with trapcode particular on them. Imagine just selecting the layers, and in the Effects panel you can just change one property on all three by sliding/typing it in. That's it, done.
That's a solution for if you want everything to be the same, but what if you just want to tweak (not link) one property across several layers with everything else remaining separate?