Maybe, if it is something you use a lot then it never hurts to stay on top of updates. In terms of changes, there's not too many major ones, but then again the upgrade price isn't that major either.
The Skydrive integration is good, as it the
touch optimisation across all of office 2013 that makes buttons easier to press with fingers.
However I actually find I use the free version from the Windows Store more than the full office one as it is quick and designed with touch in mind throughout.
OneNote app