I would imagine that most of us have several websites of our own that interlink, but we all know that linking from pages on different IP ranges to the target site is much more beneficial than sites close to or even on the same server. Now, I know that I can provide hosting for others at virtually no cost to myself on one IP, and I also know that there wil be many of you in the same boat (you may have a reseller account for example or a co-lo set up for reselling). If I swapped 5 accounts on my server for 5 accounts on 5 different servers all in different IP ranges for some simple sites, it would cost me almost nothing and benefit my linking options greatly. All I need to do is find 5 more trustworthy professionals with a decent setup. Please knock holes in this and tell me why it wouldn't work.
Hmmm... sounds like a good business idea for someone. A place where those of us with dedicated servers can "swap" hosting for the reasons you outlined. All you need is a third party to arrange the hosting swap and provide some means of security through a feedback forum or a "security deposit"... I wonder how many people would be interested in such a beast.