I agree with your points about the balance in the relationship, and how difficult it will be to show that. River certainly seems to have rather a lot written in that diary and of course we're never going to see most of it, although it would be nice to have a point where she asks "have we done this yet?" and he's able to say that they have.

Thinking about it though, I suppose one could argue that River's having all this information isn't so much tipping the balance her way as evening things up. The Doctor is always going to have the power in any relationship purely because of who he is and what he can do, so this sort of puts them on a more even footing.