If I answer you no then I'll be lying. Even though my hope is for us to see 1 btc equivalent to 1 btc some day with the price of fiat mean nothing to us, the current movement of the price still gives us the indication in how well accepted btc is and its demand. I do agree with your reasoning but until the I will still closely follow the btc price movement.
Of course, the price of bitcoin matters. Most people decided to invest in bitcoin because they expect that the price of bitcoin will continually rise then their investment will gain not to put in vain. Those people that is being paid through bitcoins in exchange of their online jobs are also concerned with the bitcoin price because online jobs is their source of income. The price of bitcoin really matter so I am looking forward for its continue success and sooner its legalization.
I'm agree with you, thus, not only for investing but especially in other transaction. If you use bitcoin for paying online it is non-sense because we can use the other currency that are most demand. Infact, they wait to increase the price (equal value to dollar/local currency) to less bitcoin will use.
Additionally, I'm sure the trading will face out in bitcoin. As a business, trading is most easily way to get an income through bitcoin. And this will the reason why bitcoin need to buy and sell, it's all about profit.