Stack Overflow is driven by incoming links—ranking SO results high in Google is crucial—and it is those incoming links that bring people to the site.
We really should take your comment about "not getting the Google juice they deserve" to heart. Stack Overflow is about making the Internet a better place and giving back.
rel="nofollow" serves a purpose but, perhaps, there is some criteria that can determine when a post surpasses the potential for wide-spread abuse and can be placed in the "giving back" column. Some combination of:
- Reputation (i.e. trust)
- User History (i.e. tracking tendency for a user to link to the same domain)
I'm not pretending to know the criteria, or even if there is a criteria. But agree with the principle of your request, though.