I've read a few articles about the 'millennial spending' trends, and what seems to be frivolous spending is actually a result of a messy economy. For example, the price of housing, healthcare and child-rearing have shot up, so most millennials can't afford houses or to have kids, and a major medical bill can be crippling. But the costs of luxury items (fancy phones, huge TVs, video game systems, computers, cheap fashion) have dropped way down, so now you have a whole generation with a great phone, wardrobe and TV, but they can't buy a house. It's sad! So I'm sure we're seeing some of that reflected in the pony market - young people who can't afford a house, but their budget has room for their collections, provided that it's something like MLP and not Ferrari.
I was friends with a collector once though, she thought nothing of dropping $1-2k on ponies at a time, which blew my mind. It was kind of sad; she had a dedicated pony room, all decked out in ponies and merch and so on, but she didn't even know basic pony maintenance. She couldn't curl their hair, couldn't pop a head off to check for rust, doesn't even know how to clean them properly; but she would spend $500 on a pony worth $100 because she didn't want to wait. It felt less like collecting and more like hoarding, since it seemed like she was mostly obsessed with the online popularity her pony room garnered her. She never took pictures of them individually, just posted pictures of her 'super expensive pony room', with all of them crammed in from floor to ceiling.
If you want to collect Ferraris, you should probably know how to put gas in the car! That's how it felt, looking at her rows of ponies she overpaid for.