Google has always liked backlinks - and lots of them - and the fact that they are from similarly "themed" pages helps a little as do about 150 other factors ranging from the title of the page to the fact that the page validates through an html checker.
The first 4 factors you mentioned really dont come into play for PR(page rank) since by definition that is the PAGE rank - not the SITE rank
- now the way a site is setup and "if" there is a recurring theme throughout the site and the linking structure is good, pages can transfer their PAGE rank around more efficiently
Most good trades that Ive done were based on:
traffic
type (or theme) of pages
my view as to whether the person is trying to spam the SEs
the WMs willingness to "network"
my take on whether the person is a hobbyist or serious
I watch the persons willingness to help others out
those are the qualities I look for - maybe cause Im old - or maybe cause my sites have always weathered any of these ups and downs and it's always been my approach - or maybe cause I think Im just right