Is there much of a penalty (ignoring price) to be had in getting a 400D instead of a 450D?
I wouldnt say so, people are still getting the 350D over the 400D now... Due to price mostly but even when it was released im sure people still went for the 350D.
So when the 450D is released it will be die hard camera fan boys who go for the 450D over the 400D.
I wouldnt pay the extra for it, i personally dont think its worth it, especially for a newbie like myself.