Heres an example if I had 15 websites which have a PR 3-5 on different domains with very different content what is the value of adding a links page on each one linking to each other? Do Google penalise or reward this?
It is always good to link from websites that are of similar content or similar theme. If you are linking for PR then there are chances that Google might penalize all your sites. You must have achieved PR with great efforts and all your efforts will go in drain so please be very careful while linking.