Sorry for resurrecting the topic or beating dead horse, but I wanted to share my opinion today when ASICS are already out there and much much more powerful ones are now on the pre-order.
I believe that coin mining is almost comparable to gold mining. When bitcoin started it was like a Klondike gold rush. A lot of lucky people who got to the river first got rich similar to a lot of bitcoin miners who mined thousands of btcs when they had a chance. Then the news got out a lot more miners jumped in for the riches and difficulty of finding any gold on the river or mine any bitcoin drastically increased. People started to bring heavy equipment to dig the gold out from deeper nodes and bitcoin miners started developing equipment to mine at more hashes per second.
In the end the gold rush ended when supply was almost exhausted and only people with the most expensive equipment could make some kind of a profit. Same happened to bitcoin. Mining btc today with anything but hundreds or thousands of GH/s is pointless. And difficulty increases every day. Unlike the real world there are different kinds of cryptocurrencies, the problem here is that BTC will be a foundation of this virtual gold mining for many years still and will be considered as the most solid cryptocurrency and considered as a trade value.
With more powerful ASICs being released on quarterly basis mining BTC will become pretty much impossible unless you have something like 2TH/s miner and then not long after that even those miners will struggle to mine any btc. Thats why there are more coins out there to mine now, but will these coins be ever valuable as BTC? Will gold be equal to silver, or silver to bronze? Unlikely. Even if you are able to mine 1000$ a day in Dogecoins because everything is based on BTC value and because you can't directly sell new type of coins your 'fortune' will pretty much be only 'virtual' and possible never realize itself into a real world money unless the cryptocurrency trade will pick up and people will be able to trade any coin towards bitcoin.
Will ASICs destroy bitcoin? No, it will only make BTC value stronger and higher. But less and less people will be able to mine btc unless they have very powerful ASIC miners and value of other coins will increase because of that. Cryptocurrency mining though is quite niche 'adventure'. Its more of an experience and a "game" if you wish than the actual business so it will never be as popular as gambling in Las Vegas for example. BTC is being acknowledged as possible currency in the world today and in time we may even be able to buy things on Amazon for BTC, but when this happens I bet that it will be VERY difficult and will take forever to 'mine' btc or obtain it for free. It may be legalized as a currency for transactions online but this I bet will lead to conditions put on miners that will limit them in some way.
So BTC will be there but similar to mining gold today you'll have to be either very lucky or will have to own a farm of rigs that will mine BTC 24/7 at hundreds of Terahashes per second to make some profit. And when 'gold mine' runs empty people will have to look for other coins to mine but they may never be as profitable as BTC if this coin will be kept as a base trade unit.