You cannot justify it on the basis of quality of results, or shooting potential. Very few photos taken by any photographer actually go anywhere near maxxing out what the camera can do. Most could have been shot on a compact TBH and be none the worse for it. If you look at the iconic pictures from the last century or so, very few of them relied on cutting edge technology, or even amazing photographic technique - it's more about being in the right place at the right time, with a great subject in front of your lens.
We buy expensive top-end kit for different reasons, if we're honest about it. Same as you don't buy a Ferrari to get places quicker, or a Mercedes to get there in more comfort. It's all about the pleasure of ownership, however that is manifests itself. That's a massively complex and very individual question, but very rarely is technical performance critical to the end result.
There is one major exception to this, and that is my own outfit. I absolutely need those L lenses and if I don't upgrade my 40D soon, which is clearly useless now the 7D is here, I'm never going to take a decent picture. Actually, I really need a 1DMk4 but becasue I'm sensible and don't like to spend money unnecessarily, I'll put up with a 7D