If I look at Allaire there are at least 12 trails defined. Who is going to rate 12 trails? This is at least 1 reason why the system doesn't work. I mean the proof to me is in the pudding. Nobody uses it. It's obviously got some issues with it.
Like Matty says, most of us see the park as a whole. Either it's worth the trip or it isn't, which is what we're trying to address here. Should I drive to this park to ride? If the park isn't good as a whole, I don't want to bother.
Individual trails would be used at a local level. And in my experience, locals aren't going to use a fine-tuned rating system to decide if they're going to ride. They know from experience what the trails will be like.
If users want a more granular discussion they go to the message board. Both to add or consume the data behind the red/yellow/green light.