Just to add a little to this great reply...
Here is how I would determine if it was worth my time to keep some of the old pages.
If the industry is the same but the end user is different, I would make EVERY attempt to keep those old pages. AuthorRank will matter in the future if you can contribute that information into a particular rel=publisher then I think it will be totally worth the time.
If, however, the information has nothing to do with the industry, then I wouldn't even consider taking the time to figure all of this out. I would have a kick ass 404 page to help people find your new stuff though.
Remember too that when you 301 redirect you do in fact loose some "link juice". (I really hate that phrase) So if the incoming links are of little to now value then a 301 will provide even less.