Grasping at Grace (and Growth)

Actually, Gaiman explained how he came up with this, and yes, the basic idea wasn't "TARDIS, personified"--the basic idea was "the one thing I really want to do now that I have a chance to write Who is to go deeper into the TARDIS." :) (http://www.guardian.co.uk/tv-and-radio/tvandradioblog/2011/may/16/neil-gaiman-doctor-who-doctors-wife?commentpage=1#comment-10776185)

So clearly, you're right. He loves the TARDIS and wants to learn more about her just as much as we do. :)

(He also expresses in the same interview that now that they have the sets for the corridors, he thinks they might be used again and other writers might show us other rooms. :) )