I'm sure others justify their spending in different ways than I. But the way that works for me is sketching. I love to sketch outfits. I don't sketch any new designs - I'm not a fashion designer - but I love to sketch outfits using items I own, items I'd like to buy or items I'd love to style with.
I'm currently lusting over the Supre Oversized Knit Top $32 in Jade. And this is just one page (the mainly black page - it's a Melbourne thing) of my sketches of how I would wear it. (I'm not the best sketcher but I sketching all the same).
I'll try it on next time I go shopping - and if all goes to plan, then it shall soon be all mine muahaha! :)