All of them. The more coins have been mined, the fewer are left to mine and the harder they are to mine.
It's guaranteed scarcity. By design. All you have to add to that formula is the idea that there's a demand. And that's what every ICO is: hype about demand for a decreasingly available thing.
Once you have been sold that there's a demand, the appreciation is guaranteed by definition of what it is.
