I did upgrade and enjoy the new features and improvements, but you're right, there wasn't much added.
My upgrade price was $20 ($10 discount if you use the link within the demo), so I think it was still worth it.
By the way, 2008 already had the disk defragmenter. 2009 adds a shortcut cleaner, some cool aesthetic improvements, and I've found its system recommendations to be handier than past versions.