With the way the Angels jerk their prospects around(see Erick Aybar, Joe Saunders, Brandon Wood), I think you may be better off not keeping this guy. Do not think though that I don't like this guy, I happen to like him quite a bit.
He has 15-20 HR power, and profiles as a utility guy in Anaheim. His swing can get a bit long, as evidenced by his 111 Ks so far this year in only 3/4 of a season as AA. This could be a concern if he is advanced to AAA next year and he faces pitchers with more experience. I would expect a couple of call-ups and send-downs next year when guys need a rest or get hurt, which in the context of your inquiry hurts his value. But as soon as 2009, I think he may have a full time gig in Anaheim, but over the next year, I think it will be an aggravating time for Rodriguez and for you, if you did decide to save him within these parameters.
Hope this helps.