The better delivery thing is not to be glossed over. Plus also having the best set-pieces in the league. Those two factors in would hugely improve an already top team I believe. He created the most chances in the league last season. They are a similar level defensively I think.
I've said a few times over the summer that I think Baines has the potential to transform our team, as I feel he has the ability to handle the width on the left himself. This will see us firstly, now have a source of excellent delivery from the left, and secondly, be able to play a Kagawa, Adnan or even Rooney on the left and allow them to express themselves without losing balance.
I think having an option which allows Rooney to play from the left effectively will transform us as a team, because it immediately allows us to play 3 central midfielders, which we frankly need quite regularly. Rooney, despite being one of our best players, is also an obstacle for our development as a team at times I think, on the basis that we feel we must play him behind Van Persie, which limits what we can do with the midfield behind him.
So basically, one subtle change, like just switching the left-back, can make all the difference in top football to me, and can have that effect for us.