I don't think the word "pristine" would apply to these aircraft. Bad things happen when you store airframes in a humid climate that features freezing conditions. Why do you think that U.S. stores airframes in the Arizona desert? Low humidity, with moderate temperature changes.
Consider for a moment that the a MiG-25 constucted primarily out of high tensile, thin gauge steel is far more vulnerable to corrosion than a comparable Western airframe built out of aluminum. These aging airframes have deteriorate far more than most people would have imagined.
Of course, conventional alloy airframes might have had some value as scrap metal.
It is also clear that the airbase appears to be neglected and overgrown. Notice the abandoned building in the first photo. In the third photo there is even a garden planted next to what appears to be a caretaker's cottage. It isn't surprising to see garden, especially when you consider that wages frequently went unpaid for years - until the current oil-funded economic recovery under Putin. Overall, this is a sad testament to the poverty and decline of post-Soviet Russia.
Pictures 2 and 3 mostly show recce MiG-25s, not MiG-31s. And the airbase is definately Rzhev, which is the main 'PVO' maintenance and storage base (at least in the West), and the rework plant 514ARZ. I visited the place in 1996, back then the place was packed with Tu-128s, MiG-25s and at least a regiment worth of cut-up Flagons, half of which were camouflaged.
TinWing, i reckon you've never seen a Russian/Soviet airbase in action, have you? They look definately far more decripit than what we're used to in the West, but why remove a bit of grass if it doesn't hamper operations? The gardens are very common on and around Russian airbases. Generally, Russians have always loved their gardens and the upkeep of them was actively supported as early as Soviet times (as it was in other WarPac nations as well. Quote from a Polish Iskra instructor: "Gardens. Puh! I want to fly in the sky, not dig in the ground!" ;D ), and it wouldn't be the first time that i've been doing my planespotting from exactly such a gardening area.
And don't make the Russian climate any worse than it is. In summers it can be blistering hot, winters are freezing, but it's actually quite dry. If the airframe is closed off properly (as the covers on canopies, intakes and exhausts show), the suffering on the aircraft isn't all that high. Remember that operational Soviet/Russian aircraft are simply put on a flightline for most of their career.
I also suspect that Russian aircraft are probably a bit more tougher and thus a bit more weather-resistant than Western designs. I seem to recall an article in some magazine several years back when the author/editor was invited to do pull-ups on a Russian fighter's pitot probe.