Seems like a mentor would be helpful in this kind of situation. I'm envisioning someone who's gone through success and failure, who isn't so emotionally connected with your project, who you can trust with the details even if they aren't flattering or optimistic, and who can help you make some of those judgement calls that get cloudy when you're right in the middle of something. A person like that is hard to find, but I think it's worth looking for.