I'm not very convinced that people who posess bitcoins are actually keen on spend it on merchandise, lets say. Most of them will try to speculate and profit and that's a very bad thing for the future of bitcoin economy. It's very difficult to invest money in such a business where the bitcoin price is manipulated. Anyway, bitcoin is a good example for people that there are better alternatives anytime, but people fail to use them due to their greed.
I disagree. The week to week changes in Bitcoin don't really matter what matters is the holding cost. What matters is the cash flow volatility resulting from the window between getting paid and exchanging for fiat (or some or all of the coins to pay your non-coin expenses). The hourly fluctuations are much smaller now and if you can't handle it then for ~2% Bit-pay will absorb all that risk for you. Sell something for $100, they give customer a price in BTC, you get $98 (after fees).