In my recollection, it takes considerable time for a leather constructed boot to crack or develop wear related problems, and fabric boots will not offer the same protection as high quality leather footwear.
My original Brasher Hillmasters i had in the 1980s, took quite a few year's until the leather uppers showed significant wear, resulting in the need for replacements.
I used to get involved with quite a few well established Challenge Events held in and around South Wales and across the bridge in Shropshire and Somerset and other counties closer to the Welsh borders.
I found that if one carefully dried the boots,after cleaning off all the mud with luke warm water, then the leather uppers would last a significant time.
Never force dry your leather boots, by placing them in a hot room or next to a radiator, and fill them with newspaper, and give them plenty of time to dry, naturally, in a cool environment.
All i used was quality boot polish, and never bothered with Nikwax or similar products, as the leather was designed to breathe naturally,and covering them with wax or such like, did not last that long, in really damp conditions.
Some leather boots are manufactured to higher standards than others, but after care is what usually results in longevity.
Mistreat your footwear, and they will not last very long, and next time your in Snowdonia, pay a visit to the Pen Y Gwyrydd hotel, as leather hobnailed boots worn on the famous 1953 Successful Everest expedition are on display.
Its the aftercare of the leather that will result in how long they will last, but all boots that receive regular use, will eventually wear out,and need replacing.