There are different ways how new feature can affect Bitcoin's price. First, there is a speculative effect - when developers announce that they plan to implement a new feature and later report progress on it, the market may consider it bullish news. I believe that the development of Lightning Network is one of the reasons why we had such a big rally in the last year. The second part is when the demand increase after the feature has been released as a direct result of that feature. For example, if Bitcoin will get better privacy, it might get more new users and the price will go up.

The problem with speculative increase is that can be only temporary and the actual usability of a new feature will determine how big the price effect will be.