My group has been playing for quite a while now, some of them through more than one character, with a few people who have come and gone. I think most of them are fairly good roleplayers and sometimes it even gets quite confrontational between them when their outlooks or goals don't quite align.
One thing I've noticed, though? None of them gives a damn about their Big Dream. Session after session, month after month, I ask the question, "Did you risk or sacrifice something significant to realize your big dream?" The answer has been YES maybe 2-3 times. Moral Codes come up and are pulling their weight. But never Big Dreams. I remind them often that they can change their Big Dreams if they don't feel like it fits. No one has done it, even once.
Maybe it's that Big Dreams run counter to the fiction you have to accept to run a campaign, especially with a bunch of random characters from very different backgrounds -- "Why does this group stick together?" Well, the answer is often simply "There wouldn't be a game otherwise." Some of the group's Big Dreams would certainly split the group up, eventually (not everyone wants to go to Uzbekistan, go figure).
But basically I keep coming back to this issue where Big Dreams are really not pulling their weight when it comes to creating compelling roleplay situations, driving the campaign, or anything else. Have you run into this in your games? Or, if not, any idea why not?