I'd say it's a prominent feature. Calling any particular theme an integral part of a work of fiction is restrictive and allows your expectations to dictate your perception.
How many of the historical episodes since the revival have been set in Victorian GB? It's got to be close to half. Retreading the same social setting again and again doesn't really help matters as far as aesthetic content informing thematic content goes (though I didn't mind the last ep because it wasn't afraid to go all out with the cheese). Hind was a good way of bridging the divide I think, with the right types of characters and blend of sci-fi and supernatural horror, but it sort of fell apart towards the end and didn't do as much as it could have with its premise.
I too greatly enjoy speculative fiction, but I also recognise that it's not a defining element of modern Doctor Who. Forewarning: this is going to sound confrontational but that's mostly due to the desertion of my eloquence. Browsing these threads on and off for the past few years it seems to me that frequently you do what I mention above and allow your expectations to dictate your perception. That's why I asked if you value social commentary above entertainment value, as it seems (once again, to me) that even paper-thin attempts at social or cultural critique are enough for you to hold otherwise mediocre episodes in esteem (here's looking at you, Gridlock). OT: Full disclosure, I do this myself, particularly with games such as New Vegas or Bioshock, but that's generally because a) this sort of thing is rare as hen's teeth in high-budget interactive media and b) they're willing to even attempt to wed their gameplay to their commentary, which is even rarer. What strikes me though is that I can't think of a single episode of modern Who that tackles these sorts of issues as thoroughly as the videogames mentioned above, which to me is a little dire. The limitations of the 45 minute episodic format play a large part in that, I reckon.
One other thing I feel I must say is that the lengths you go to to point out racist or right wing undertones in the show borders on the insulting: many of the occurences you list are so contrived that your decrying them comes across as though you're actually decrying the viewers who failed to note them as less enlightened than yourself. You acknowledged you went overboard with regards to the salvagers in The Journey to the Centre of the TARDIS, but recently you also did it with the submarine episode. I can't help but feel that if you spent less time searching for otherwise innocuous elements to justify your criticisms and treated episodes with social inquiry as a bonus and not an entitlement you'd enjoy the show more.
All that said, I generally enjoy your posts and would strongly agree with your last paragraph if you hadn't included Gridlock in it