All this hoarding does nothing for the bitcoin economy.
Well, not quite true.
Let's say an item I need is priced in dollars, and the price is $10. So if I prefer to pay for that purchase in bitcoins, I then buy $10 worth of bitcoins. It doesn't matter what the exchange rate is. If BTC/USD is $10, then I need 1 BTC. If BTC/USD is $2 then I need 5 BTC. Either way, I am exchanging $10 of fiat to get $10 worth of bitcoins.
So in that context, you are correct. Hoarding does nothing for the bitcoin economy -- it doesn't hurt nor help.
Now if I am a Bitcoin-related entrepreneur I might hold bitcoins. And I might be looking to raise funds for my entrepreneurial ambitions.
If there is hoarding of coins and the exchange rate rises quite a bit, my coins have more buying power as the result of others hoarding.
Thus hoarding helps the undercapitalized risk-taking entrepreneur who bought or mined bitcoins for speculation earlier.
At the same time, an increase in the exchange rate due simply to hoarding increases the risk of a price collapse. If that demand isn't due to those bitcoins being used in commerce for buying and selling, then many hoarders have greater control over the exchange rate. There was a nearly 30% drop in the exchange from the October high to October low. During that time there probably wasn't a 30% decrease in the use of bitcoins for commerce transactions so the bulk of that move was speculative buying and selling (mostly selling). If there wasn't hoarding the price probably would never have reached $13, and thus the drop wouldn't have been as dramatic.
This exchange rate volatility, which can be attributed to speculative activity (hoarding) then actually does do something for the Bitcoin economy -- it hurts it, at least from a merchant's perspective. A merchant doesn't want to see the profits from a sale vaporize because the currency rate took a turn south. As a result the merchant will use a payment processor to convert those coins to fiat, which add costs (which makes Bitcoin less favored for commerce) and also lessens the likelihood that the merchant in turn will use those coins for its purchases.
The thing is, ... there's no "right" way. Bitcoins function as a store of value, and they will be held for speculative purposes by those willing to take that risk.
No matter what payment method is used, a merchant -- especially one starting with no customer base, has a very tall hill to climb. That some investors are holding onto bitcoins should really be of little concern to that merchant.