Let's be absolutely clear: your coins are only worth what someone is willing to pay. And when the one and only true "run on the bank" of one of these currencies happens, it will happen within the span of less than an hour. All these people who are buying to eventually cash out are going to blink and wonder what the hell happened.
Take BTC as the example right now. All over the place, people are showing regret for not buying in a few years ago. No average BTC "shareholder" is going to be able to cash out for more than mere pennies. The majority of coins are owned by big players, and you are effectively dumping your cash into their pockets by buying into it.
BTC's Nakamoto "promises" they will never cash out their enormous share. How nice of them. The community can monitor Nakamoto's wallets all they want. I can't wait for him/her to cash out their BTC, and screw over the entire system. I'm just sitting here ready to laugh.