Yes, pretty much the idea I had. Then it is supposed that when all the bitcoins have been mined, price will be stable based on true demand - supply basis, correct? But until then, we need some kind of measures or regulations (not based in a central entity) to avoid speculation with bitcoins, because it is truly affecting Bitcoin's growing and its reputation as an alternative currency.
It doesn't depend on what percentage of coins have been mined, but rather how deep the market is. "Mining" is merely an inflationary pressure and it's a given, so it's not a source of volatility. What you need is stable demand. An increased number of speculators with different interests and increased commerce means the market will respond faster and stronger to pressure.