Their low cash-value is probably almost wholly due the difficulty in getting cash for them.
Deflation of bitcoins can effectively be infinite, but should slow significantly if/when a significant amount of people get in on it and start using them.
I think it would be enough to jumpstart the process if one service that already reliably trades virtual currency for money (say, EVE) were to start accepting bitcoins for the purchase of said virtual currency.
But, given that there are very few means to cash out into other currencies, and the products one can buy with bitcoins are extremely limited and generally virtual goods, it's still wildly speculative that they have any longterm value.