Or it's an interesting opportunity to explore a facet of the Doctor that we've previously taken for granted.
I already find it compelling that a month after the Doctor rewrote his own history (in viewer time), he'll be forced to look in the mirror everyday and see the face of a man he broke the laws of time to save... a man whose family didn't do so well in the long run, according to RTD. What does that say about the Doctor's decision to save Gallifrey?
I've always thought a story could be told about the Doctor's faces. Why did 2 have the face of Ramon Salamander? Why did 6 have the face of Maxil? Are the faces random or do they appear with a purpose? It probably isn't a necessary bit of the lore to dive into... but we also didn't really need the TARDIS to explain why she never takes the Doctor where he wants to go. And I thought that episode was marvelous.