1. Each Episode Would Have More Screentime
One issue that gets dragged up these days with Doctor Who these days is that the storylines tend to finish on a rather hurried and abrupt note. Indeed, Terry Pratchett has criticised the series for its tendency to tie off narratives with a spontaneous deus ex machina, or as the Doctor himself calls it, doing a clever thing. This niggle is likely one that the writers are aware of: think of the scene in The Vampires of Venice when the Doctor saves the day by just turning the evil device off! This was probably intended as self-referential humour to address past episodes. However its not something you can do a lot about when youve only got 45 minutes to wrap everything up. Even with two-part episodes, while it is easier to structure the stories, there is still an obligation to work in the big cliffhanger before the 45-minute mark. It seemed to me that the recent episode The Power of Three could have benefited from a bit more screen time to conclude the narrative thread than the five minutes it had left. If, on the other hand, the stories were written at their natural length and divided over a couple of weeks, it would only be a matter of finding a suitable advancement of the plot on which to end each instalment, and the writers would be given more of an opportunity to work towards a satisfying climax.