Basicly first thing that made me want to play and is definitely important.
Dark night, big forest, wild animals everywhere. Felt almost like in Gothik 1. (old times ,old times)
So basicly I just though: How about developing the forest a little bit more?
Say maybe, make it more dangerous. More bloodthirst animals! Like wolves or wolverines. Would be good, ALTHOUGH people use Enders. My thoughts are, why not implement some little bonus for not lighthacking enviroment/highlighting animals? (dunno how are you going to do that- maybe make some modified enders aside of normal official client? that is of course if Enders agrees since the code is his) Maybe 10% more LP for not using it constantly for 3 ingame days? The effect could be activated at any time and would last 1 ingame day and would pause on logout. Or something like that.
Then a player would feel it's both profitable and climatic to play in the dark and without magical instict telling them where are the animals at any time.
Aside of that basic idea, maybe implement some other way to notice animals, an option that would work like prospecting, would take 4 secounds and spoiling the locations of animals. More realism, possibly more climatic, than when using Enders highlights.
From expirance I can also say that weather helps to build up climate (e.g. Minecraft), especially when playing in the wild.
Also post your own ideas, modify mine and feel free to comment.