I too am culing what has become a bit of a burden of a collection, I never complete them and then if I do I don't use them so I'd like to pull it down to a more managable number. I think the advice of sell the ones you can 'easily' replace is pretty good, I am holding on to the bikes that either mean something (Salsas I have had for a long time, and known all the owners of through their lives!), or are just not possible really to replace (ie Zinn disc). It feels pretty good to go through and move things on, even there is a weird reluctance to let go of things jus in case they come in useful.
I sold a frame and some wheels this week in fact, so I'm getting there*
*OK, fine, I also bought a whole bike, but that was really for my son (in ten years) and it was such a good deal, and I won't keep it all, and its very rare, and....