Hello jbullet, and welcome to the forums.
The first observation - this is not something Google wants to reward. No doubt they see it as trying to manipulate search results.
I know of several cases where this tactic was tried. Sometimes Google catches that there's a new owner for those domains and resets the to zero, and the purchase price is essentially down the drain. In other cases it seems to work out.
I've heard of cases where the newly purchased domains just operated as is for a few months. Then some links (not redirects) were introduced to the owners other domain. And then slowly, eventually, a full 301 was introduced. In those cases, the PR seemed to be preserved. And yet, in a similar case the new owner actually got a penalty.
Google knows people do this and as I said, they don't really like it. Why it works sometimes and not others - what makes the difference - is not 100% clear. I've heard it described as a "risky dance" you've got to play, and there's never a guarantee.