I hear comparisons and speculations all over the place, but I think it will just boil down to trust and exchanges.
The gold and silver market is highly profitable and people are investing in it all the time, yet, there are no stores (that I know of) here in the U.S. that excepts silver or gold. I can't pay rent, buy a cheesburger, or get a coffee with my silver any more then I could with my bitcoins or litecoins. People just trust these metals as a valued wealth. Why wouldn't they? There are hoards of people ready to buy these metals, tons of exchanges, and a cash-for-gold on every city block.
If enough people trust BTC and LTC their prices will rise and stable to accomodate mining costs and demand from investors. As far as a usable currency , shops could help a lot, but really it is all about exchanges willing to trade for your country's currency. If exchanges are willing to accomodate LTC, and people are willing to buy them, I could see Bitcoin ASICS making Litecoin value take off. Currently, I feel that if BTC-E closed down, Litecoin wouldn't last 2 months, just as if mtgox went down I couldn't see BTC having a value of more then a dollar or two. People would have a disconnection with the perceived value of the currency, and it's trust would suffer.
+1 to all but the bolded.
Someone could just open up another exchange and everyone would move their coins that weren't on the exchange that got taken down to the new one.
Solidcoin did that multiple times. The reason they failed wasn't the closure of exchanges. It was the horrible PR RealScam kept doing.
I meant the health and abundance of exchanges overall really. If the average person can't trust an exchange to trade in their p2p currencies for their own country's currency, then most won't bother. If btc-e and mtgox close down tonight, I'd have an immediate dismal outlook on the coins, and it would require a lot of work on the part of a 3rd company to pull in the trust and support needed to keep the idea running. I don't even know of another exchange except vircurex, which seems shitty in comparison (although somehow it shows up first in google for me).
I guess as transactions pick up, and exchanges start making actual money, we'll begin to see a lot more. I'm betting exchanges will quickly turn into online banks with credit cards real soon. Too bad they'll be screwing us on charges and fees just like the dog shit services that we have now already do.