Simulations are good and funny, but not games. Flight sims at last are not really games or not really sims. Ok, car racing games are really a working hybrid of game and simulation, but I'm talking about more complex,living simulations.
Car racing and flight sim fans would care to disagree.
Emergent behaviour is fun, but only if you know what and why it happened. Therefore often developers are impressed by emergent behaviour, players without background knowledge do not have the chance to understand the behaviour, even it is logical, it seems often to be a bug.
I agree that granular simulations are usually surplus to requirements. However I do think that simulations with a degree of LOD could be worthwhile. For example, simulate animals nearby in a granular way, and for other areas simply simulate broad predator/prey dynamics and migration patterns. I agree that emergent behaviour can be tricky. Perhaps truly emergent behaviour is not desirable, but rather representative set pieces, e.g. if a herbivore runs from a carnivore the carnivore should always be coming from a direction that the player can see.
I've played around with this approach in my game, including a need based logic to control the behaviour of entites (herbivores, carnivores, interesting objects on the ground, the player as intruder, all entities needed food and water etc.).
But overall I would welcome some sort of nature simulation as a source of new types of "random" encounter and to avoid that creepy "all these creatures exist only so you can kill them" feeling.
The first effect was, that it got quite complex really fast. The reason is, that a simulation get unstable quite fast. First all seems to work, suddenly all animals are dying around you. Was it a bug ? No, the water sources could not supply all the animals.
After fixing all the issues, it got really messy. You see some unlogical behaviour, same question: is it a bug ? After analysing several logs you discovered that this behaviour was correct. That's fine, but the major issue was: the resulting behaviour was not funny at all, but boring.
One of the most successful games (and game-simulation) with emergent behaviour is dwarf fortress. Checking their forum, you will discover quite fast, that almost every emergent situation is discovered and discussed by using the log as story. This is not a bad thing, but not always suitable for every game type (do you want to check several pages of a log to understand why an opponent has discovered and killed you in a FPS, although you were sure, that you were hidden from his view ? )