I would say that 3500 is a lot of money, and you need to make a wise decision prior to buying any bag of that price tag. If you like the leather version better, then go for it. 3500 is a lot of money to "only" buy a bag because it is cheaper than its leather counterpart.
My experience with quality:
I have never owned any denim bag, but I have been collecting various luxury bags for many years. My advice is to go after the bag you like and not because one bag is cheaper than the other. As of quality, according to my experience, leather or not, luxury bags are fragile, are prone to colour transfer, need to be protected from rain and small accidents (i.e. people bumping into them, bags fall on ground, coffee or wine is spilled in a restaurant...). Some bags, although they come with expensive price tags, would be of bad quality. You need to like the bag, because the quality can disappoint. I have a H Birkin, and it showed corner wear after only 2 months of wear. There is never a guarantee to keep the bag at the same condition after use. The B also picked my hand cream on the handles, which made them darker. I have a Fendi peekaboo, and the corner wear came even faster than on the B. Unfortunately, with or without bags, life happens and even the most reputable houses and craftmanship can be damaged, or suffer from wear and tear. Just buy the bag you like, use and enjoy it.
