Justifying the price of shoes or anything is rather difficult. It is very easy to say how much something costs, what it's worth becomes somewhat subjective. I would think that most of us that contemplate shoes in this price range, we are probably looking at the aesthetics rather than the practicality. It's how they make you feel when you wear them. Tastes vary between us all. I have seen bespoke shoes costing many thousands of pounds on this forum (different thread) that I wouldn't give houseroom to regardless of how they're welted or how much they cost.
There is something about a high end shoe that transends functionality and IMHO becomes art if the proportions are perfect.
G&G seem to appeal to me time after time, more so than most. That you pay a premium for that elegance seems correct and proper. Whether that premium is too much for the humble GYW shoe is something only you can decide.
It's for some of the same reasons why someone chooses to buy a Rolex instead of a Timex, or better yet a Patek instead of a Rolex in this case. They all do the same thing. It's just that one does it in a more.elegant fashion.