What gives a classic it's value?

A recent spate of trademe auctions has me wondering. Some classics seem to attract consistently high values and some do not. I suppose there are all the usual factors like rarity etc, but I wouldnt exactly class Apple II's as that rare - certainly not as rare as some of the other classic's (in my view anyway) I've seen on trademe go for a lot less lately. I suppose in a lot of ways it's about being in the right place at the right time. If you catch the imagination of a buyer willing to spend some dosh for nostalgic reasons, then I guess theres no telling what something will go for.
Maybe its something to do with brands that are still a going concern today? Should that make a classic device from one of these brands more or less valuable?
Maybe its investment collecting? But how do you decide what is a good investment? Clearly an Apple I board is, but I doubt there are as many clear cut cases as this. And will investment collecting ultimately pay off? I mean if you look at the purchase price of an classic at the time it was new and compare it to the price it fetches today, how long would you have to wait until it reached its original purchase price or more? Or does that not matter? Or is it not that simplistic?
It is a boogle.
Maybe its something to do with brands that are still a going concern today? Should that make a classic device from one of these brands more or less valuable?
Maybe its investment collecting? But how do you decide what is a good investment? Clearly an Apple I board is, but I doubt there are as many clear cut cases as this. And will investment collecting ultimately pay off? I mean if you look at the purchase price of an classic at the time it was new and compare it to the price it fetches today, how long would you have to wait until it reached its original purchase price or more? Or does that not matter? Or is it not that simplistic?
It is a boogle.