Rode the new bike again today, now back to back with my 2008 it is indeed an improvement.
The new engine is noticeably smoother, will drop down a few hundred RPM lower and rev out 500 rpm higher, I would guess it has a bit more bottom end, a bit more top end and a slight improvement in the middle (where the 08 engine is already pretty decent)
I would not pay a lot to upgrade just for the engine, but if looking for a new(er) bike would certainly say it is worth paying a few quid more to stretch to a 2010 if you can, but not if it means getting a less pristine, or much lower specc'd example.