I've commented on this before, but I don't remember where the thread is now (and I can't remember what I said). I'm into leather care in other areas (nothing naughty, vicar, mainly just shoes, and I used to make leather razor strops). There are plenty of oil/wax based leather treatments which help keep leather supple, waterproof to some degree, minimize cracking and lengthen its lifespan - common cheap ones include dubbin, mink oil, neatsfoot oil. In my view, pick any of those three and they'll be just as good for a leather saddle's comfort and longevity as any more expensive products. I do use more expensive products for some shoes, but it's mostly because I think they give a slightly better look (and in some cases I want dyes in the products too).
Speaking of Brooks saddles, I'm definitely a convert to Cambium these days. Mine seems to have all the comfort of my old B17, with no breaking in and no leather treatments necessary - longevity is the only thing I can't assess yet.
I definitely do seem to have a Brooks bum, but I'm envious of those who can do long rides for years on £20 saddles. The closest I've come is a Charge Spoon, which I find very comfortable for 30-40 miles. After that I start to feel pressure building up and I'd say around 50 miles is probably the farthest I'd like to go in one day on it. I'll probably get a Cambium for the bike it's currently on, and move the Spoon to a bike only used for shorter rides. The Spoon is excellent value, mind, and seems well made.
As a final note, all my saddle thoughts are based on my never using bum pads. Finding a saddle that suits my bum so well I can comfortably ride all day on it without padding (as I can with my Cambium) seems like the ideal.