One thing people tend to forget: The difficulty rise is already priced into the market rates.

In other words: All people who trade BC know that the difficulty will rise and thus they already considered it in their decision to buy or sell BC.

Thats very common in stock markets: There are often situations where a company releases very good raised earnings - and still the stock of the company goes down? Why? Because the people who buy/sell stocks always have expectations in the future - and those expectations determine the price, not the current situation of a company or a commodity.

With BC it's the same: The current price is based on expectations of BCs future, not the current "state" (like difficulty). And since everybody already expected the current difficulty jump (and also the next etc), those informations are already considered in the current price. It only has an impact if for example the next difficulty jump is much higher or lower than expected (or other unexpected things happen).