Does buying bitcoins and not spending them have negative influence of the bitcoin price?
Every investor has a different threshold for risk tolerance. A price one investor might consider as cheap, might be expensive for another investor (read Greater Fool Theory.) If the investor base of bitcoin is considerably large, at any point in time you are highly likely to have two parties trying who will be willing to take opposite positions. Improvement in liquidity, introduction of new financial contracts (futures, derivatives) can go a long way in helping improve the price volatility in bitcoin and attract a wider base of investors.