score:5
I've been planning on doing it, and reading quite a few forums, the Facebook group, and speaking to locals who have done it. The one thing they all agree on is DO NOT walk back down the Grind. They specifically urge other runners to tell off people walking down, as they get in the way, damage the track as they slip, and on top of that it's brutal on your knees and can easily slip and injure yourself.
I spoke with my roommate and she mentioned the BCMC Trail and the Baden-Powell Trail, but her understanding is those are also 'technically' one-way (up) and you may also upset people if you go down that, apart from risking your body.
It sounds like the Skyride back down is pretty scenic and recommended. If you were staying longer you could get the annual pass ($99) but for a once-off, Skyride sounds like the way to go.
[edit] Having now done it, I can confirm that some people will turn back at the 1/4 marker, as it's wider and easier and gets steeper after that. But almost nobody is seen going down after that. And I can confirm people were telling off the one or two runners who were going back down the trail. It would certainly damage the trail.