One reason to get rid of a 2003 is the IMS, but you are already getting that fix done. So, you have to ask yourself, why are you thinking of getting a new car? I went from an '02S to an '09 997 S Cab in Nov. 2009. The two driving factors (no pun intended) were the IMS concern (mine already went while under warranty), and the fact that we were in the depths of the auto doldrums. Tried for an '09 Boxster S, but dealers weren't dealing for some reason, but were on the 911. I made them an offer I thought they wouldn't accept, but did. It is a much different car. I'd suggest driving a 911 to see if it is your cup of tea. My wife likes it better for roadtrips due to being able to put stuff in the backseats. While I do enjoy it, someday, there maybe another Boxster in my garage, but that is far, far off, as the 911 still floats my boat. I'm not yearning for another car at the moment, and, knock on wood, the car has been bullet proof. The build quality seems far more superior than that of my '02 S.
Good luck. When you look at it, though, no matter what you do, it'll be a no-lose decision.