Well, @timsk you ask the right questions.The point you make (quoted) is clear enough, but isn't the value of cryptro' offset by the abillity to create a new digital currency at the press of a button at any time?
What Bitcoin did, or rather solved, was the problem of how you transfer/exchange value (coins or parts thereof) without a bank or 3rd party involved. It did not address, or even attempt to, the added value that could be implemented by adapting the technology in specific ways. This is what other currencies have done.
Yes, any Tom, Dick or MasterOfCoin could (and do) create new cryptocurrencies. But whether they subsequently have any value or not is a reflection of their usefulness and widespread adoption.
Thus, new currencies that facilitate something useful or solve existing problems will do well and gain value.
And if they don't, then no one will use them and they die.
But much as the introduction of a speedboat has little impact on global shipping, new specialist coins generally have little impact on already established coins with large numbers of users.