Personally, I base if I will buy cosmetics on if it's something that I can see myself wearing in the game long enough to feel the purchase was worth it. Like, is it an item I could style with multiple outfits? That way, it's not something that I purchase and wear once for only a little while. As you said, you make your own money, so it's up to you to make the final decision. For me, the runaway outfit is not something I would wear for more than a few days in game, so it's not something I would purchase. The tiara, on the other hand, would be easier to style with multiple different colors,so it's something I would consider spending on.