This still does not address the inherent deflationary nature of Bitcoin. As anyone who is currently hoarding their coins knows, there's very little that could tempt you to spend them, as they go up in price, and basically, always will. This has it's own set of economic problems.
I've recently answered a similar concern in someone else's topic, but it's worth repeating. The thing you're missing is that you're only thinking from the perspective of the spender, but there are two sides to every transaction. As a prospective buyer, yes, you want to hold onto your deflationary currency. By that same token, vendors want to get ahold of that deflationary currency. If a vendor agrees with you about how the value of a bitcoin will go up over time, they have every reason to give you a discounted bitcoin price below the dollar price because they believe they'll be able to make up the difference as the bitcoins they receive go up in value down the line. At that point it's just a matter of whether the discount is big enough to attract your bitcoin spending and that takes us back to the conventional decision-making issue of whether a purchase is worth it to you. Do you want to pay $4 per gallon for gas in US dollars or, let's say, $3 per gallon in bitcoins?