Looks like I'm getting that same old drum out again...
Doctor Who is a cheap show (for it's genre). Always has been; always will be. Currently it seems the BBC wants it to be even cheaper as they decided not to spend the money on producing 28 episodes for 2012/13 (which has been the norm since 2005, barring one year), commissioning instead 16. (series 7a&b, +2 Christmas episodes, +Anniversary episode)
On top of this they have also declined to recommission other relatively expensive (compared to say, soap operas) fantasy shows such as Merlin. This is the reason that the Mill has gone under, as mentioned above. The BBC are effectively cutting back on fantasy.
So, with the BBC's current attitude, you can expect the production values to drop along with the episode count.
Doctor Who is a cash cow to them, not something they want to significantly invest in.