A really cool guy I know had this to say about the topic:
"It's known as a market bubble, pretty much anything that involves money and buying shit has a bubble. It means that when a certain product is 'hot' on the market, demand for your hot item supply grows exponentially. In respond to this demand, people start gathering up or making that said supply in large quantities, and raising the product's price to above its perceived value. The product sells like hotcakes for a short period of time, but soon the market grows tired of either the product or its overstated price. Eventually people stop buying this product as its become too over-valued. interest drops. however, the people selling the product are stuck with an inventory that they can't sell for their expected price. When you have an over abundance of product with little demand for it, the bubble bursts. the people hoarding the product are essentially fucked, and end up selling off inventory for usually less than what they paid. It's a trend that's been seen in stocks, housing markets, toys, collectibles, cars, everything. and you know why it keeps happening and repeating in the same basic pattern? Because people are fucking idiots.
That's my perception of it anyways, I'm not an economist haha. As far as oldschool video games go (age and brand play a huge variable of course), they're getting pretty hot right now. The bubble is inflating with the many people gaining interest, and I'd think it's due for a burst within maybe 3-5 years."