OK, so to get Shaq (a 1-year rental of Shaq), we'd have to trade for him. Let's see a trade where we send out enough cash and assets to make it happen... and then how that situates us for the summer of 2010 (you have a valid point that trying to have a ton of cap room in 2010 is a legit strategy). My thing is, I don't think you can come up with a scenario where we are better off doing that.
For instance, you say "where we have a team FAs would want to play for". But, in your scenario, we gut our team to get Shaq, who has said he will retire after this contract. I just don't see how gutting our team for a 1-year rental of Shaq does anything for our prospects in the summer of 2010 (when our team would be Shaqless). We would have cash, but we would likely suck.