The one thing that treating a whole world as one character suffers is that it continues the treatment of a world as a "room/encounter in a dungeon". This is a bit problematic in that it is very reductionist.
This is less of a problem if you are goi9ng to run a star trek kind of campaign - "what problem will we encounter this week?"
Have you read Diaspora? You might want to. It has a treatment of this kind of activity that involves the players explicitly. You can have a sticky beak here: http://www.vsca.ca/Diaspora/
Inspired by Bobo's Sig
Rule 6 of Kurt Vonnegut's Rules on Short Stories
Be a sadist. No matter how sweet and innocent your leading characters, make awful things happen to them — in order that the reader may see what they are made of.
from Bagombo Snuff Box.