I wonder if the license allows giving away an older version if a person buys the full version instead of taking the upgrade path?

Even if the license doesn't, other laws may take precedence, such as the first sale doctrine.
http://en.wikipedia.org/wiki/First-sale_doctrine

Ideally, there should be a discount on the upgrade price as well as the full version.

My visual indexes of Poser content are at http://www.sharecg.com/pf/rgagnon