Locking your bitcoins away and not using them is the best way to ride out the highs and lows of the market if you expect the value to keep rising into the future.
But consider this: if too many people take the 'lock up and hold' approach to bitcoin it effectively reduces the usefulness of the commodity for commerce. There is some tipping point where businesses would say 'not enough bitcoins out there, let's use something else'. It's difficult to envisage a future where there is such high demand for bitcoins that traders are willing to pay huge fortunes for one.
And what exactly would be the tipping point that says "not enough Bitcoins out there, let's use something else?" If there were 2 times as many Bitcoins, and each block rewarded 100 (now 50) BTC, would this point occur any later? How about 10 times? 100 times as many Bitcoins?