14 gallons * $3/gallon * 4.5% = $1.89 / year cost keeping my tank full all the time as opposed to running it dry and buying just enough to get to work in the morning and just enough again to get home in the evening.
After 9/11 I bought a few gas cans (22 gallons total) that I keep filled in my garage for my "tactical petroleum reserve" just in case gas becomes hard to buy for a short time for some reason. After hurricane Katrina I learned my lesson to never let my tank get below half so I can drive about 200 miles without worrying about where I'll get gas if I have to leave town right now.
(And don't tell me about stale gas in my extra cans. I fill my car with them and refill the cans with fresh gas regularly.)
Like every other part of this discussion, it seems like chicken feed until you multiply it by 100 million or more drivers. I see no need for me to hoard gas. I do think many people respond by panicking and hoarding and topping off. That does produce inactive reserves and boosts demand and prices some. It is a factor. That's all. Everyone has to respond according to his own situation.