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?
Your interpretation of the merchants desire is incorrect because you are projecting the motivations of speculator onto the merchant, but speculation and being a merchant are incompatible uses for money.
A merchant makes his profit on a retail markup or on the added value of a manufacturing process (say for example someone who knits socks turning cheap yarn into a valuable sock) or both. In both cases the merchant is trying to achieve maximum TURNOVER of stock both in manufacturing and in retail setting. A merchant dose not want to sit on money waiting for it to appreciate in value so it can once again be turned into stock to be processed and or sold. Sitting on money is exposing them to the huge valuation fluctuation risk of BTC but even if they never suffer any loss in a crash they are suffering a massive reduction in turnover. Instead of going through the loop of acquiring stock, selling stock and buying new stock as quickly as possible they now have a loop that has a long period of sitting on money before it can be converted into new stock. This slower cycle means that the merchant must be making more gross margin on each iteration of the cycle in order to cover overhead costs and to make his final profit large enough to be justifiable.
Speculative holding of money and being a merchant are thus incompatible methods of making a profit, the more you try to do one the less you engage in the other, think of it as the Heisenberg Uncertainty Principle of economics "The more profit you make from speculation the less you make from Merchanting and visa-verse". The proposed discounting and hold strategy you propose is a messy mix of the two and represents a very dangerous phenomenon as it moves more people into the speculative side of BTC and away from the real commerce side, that can only end in ruin.
