Hi Richard!
Some data points from this end...
I think rider posture has a lot to do with how the saddle shapes over time. I prefer a 45° back angle (with hands atop the brake hoods with drop handlebars), so I place about as much weight on my hands as I do my bottom, putting less load on the saddle than if I rode more upright. I place so little weight on the saddle, I've had to go with lighter elastomers on my Thudbusters and found I could not actuate the springs on my past Brooks Flyer and Conquest saddles, so I sold them on. For this reason, my saddles take a long time to break in. I much prefer them to have their original dome shape, so when the sit-bone depressions get too deep (and the center ridge too pronounced) for me, I sell them on. At worst, my sold-on saddles look like your Third photo.
I never or almost never adjust the tension bolt on my saddles. On the rare times I have, I have done so very conservatively -- no more than 1/4 turn at a time. The problem, I've found, is the tension bolt tends to exacerbate the formation of a central ridge the length of the center-top, making the saddle into what Jobst Brandt described as an "A** Hatchet", one that causes perineal abrasions and discomfort in my use.
I'm a bit leery of using too much Proofide and do so only sparingly. I do lightly coat the rough-cut underside of the saddle only once when it is new, then apply the lightest of coatings thereafter to only the top hide once every couple of years or so. The saddles and bikes are stored under cover, so are not exposed to hot sun. I've had no problem with the leather drying or cracking over time. On my desert tours, I do cover the saddle to protect it from the direct rays of the hot sun when the bike is parked.
I always use a rain cover if there is any hint of rain, fog, or dew. Sometimes I use a couple covers after one bad experience with an incompletely sealed seam. I now prefer waterproof saddle covers with no top seams for this reason. While I prefer a "real" dedicated saddle cover for parking, I will often top it with a disposable shower cap or heavy duty double-wall plastic shopping bag in an effort to disguise not only the saddle brand but my underseat tool bag (to better discourage theft).
My string of rail breakage seems to have ended with the switch to powdercoated rails. Brooks went through a period where their subcontractor's chroming process was faulty and the rails became hydrogen embrittled. I've gone through four...no, five chromed Brooks saddle rails. I've had no breakage since switching to their powdercoated rails. Once you develop the knack, it is surprisingly easy to swap the leather cover onto new rails -- and much more economical than a whole new saddle. One of my covers is now on its third set of rails (photo below). This last powdercoated set has outlasted the previous two chromed ones by a factor of 2x. For more on saddle rail breakage and replacing rails, see:
http://thorncyclesforum.co.uk/index.php?topic=6369.msg38415#msg38415 I've found a combination of rough roads and the saddle cantilevered over the clamp can increase the risk of breakage. For this reason (as well as for fitting purposes) I early on came to prefer long-layback seatposts because they place the clamps more centrally on the rails. Otherwise, I find a conventional or zero-offset clamp is located pretty far forward on the rails and my weight is placed on the rear. Each of my broken rails occurred at the rear of the saddle clamp. Although the primary cause of my breakage was due to improper chroming, it is no stretch to imagine that a rider's weight bouncing atop the rear of a laid-back
saddle on rough roads is more likely to stress the rails at just this point, so it is better the clamp is centrally located if possible via a layback
clamp design (keeping in mind not everyone will fit a seatpost with a long-layback clamp).
I've found my Thudbuster suspension seatposts are kinder not only to the saddle rails, but also the leather covers. They absorb the sharp impacts of big bumps and so shield the saddle from the full force of impact. I find my new saddles mounted to the sus-posts take longer to break in and the older saddles last longer before needing replacement.
The kind of saddle clamp makes a big difference to saddle rail life. As Brooks urge, it is best to avoid "rail biter" saddle clamps with built-in stress risers in favor of those that fully support the rails for the entire length of the clamp.
Brooks saddles are handmade from leather, a natural substance. I've found the individual cuts of leather can vary greatly in stiffness and I've had a couple that were fully broken in at the 200km mark and then just sort of dissolved from there. Others of mine have stayed firm until they accumulated about 10,000km (yay!), at which point I moved them on. It really does vary. My B.17 Champion Special is thicker than usual and has skived edges. It remains firmest of all, not unlike your own thicker Select, Richard.
I've brought a number of misshapen old Brooks saddles back to life or others. Usually when the sides start to flare, early intervention with a hole punch and some lacing will keep the sides vertical and prevent the saddle from spreading. If the sides start to flare, then the back starts to "break" and develop a swale. At that point, the sides simply spread more in a sort of vicious cycle. It is well to remember that for many, this is the point where the saddle becomes most comfortable of all (just not for me; we're all individuals, after all). I would find your saddle as pictured in the last photo of your link to be well past worn out for my own needs. Vive la diffιrence
In extreme cases, I've followed the technique of my late friend Toshihiko, who perished in a train collision last Fall. He would detension the saddle -- usually popping the nosepiece free of the tension bolt first -- and soak it for several *days* in a bucket of room-temperature water. After, he would remove the saddle, allow it to drain, and then pack the now very soft and pliable leather with rags and newspaper and clamps to restore the shape, changing the rags and newspaper daily. The results were amazing and to my utter astonishment the saddle not only survived but looked remarkably new in shape and presentation afterwards needing only minimal retensioning and a light Proofiding. Even more astonishing, it held its shape while riding. He liked the old Ideal 90 saddles, and it is rare to find those anymore in anything resembling good condition, so every one he had was brought back from the dead in this way.
All the best,
Dan.