Interesting post and more fuel to the fire that bartering or buying based on PR alone is a fool’s errand. You definitely need to do more research, just a couple of other simple steps is all that is really needed:
1) Does the site rank top 10 for their full Title. Most sites in this industry have crazy long keyword stuffed Title tags, which actually makes them fairly unique search terms, so a competitive site should show up high on the first page of Google for a full Title search.
2) Does the site rank in the top 100 for any of the keyword phrases they are targeting. Look for 3 word keyphrases that should be easier to rank for.