If I buy a car for $15,000, I pay $2,250 in taxes ... Multiply that by 280 Million me's, and you could have a sizable drop in consumerism
Let's presume that the 280MM Austins average $35K/yr. Without a federal income tax, that's an extra $7,700 cash in their pockets each year! Those car taxes dont look quite as daunting now.
Furthermore, your assertion that sales taxes drive down spending is not always vaild. The spikes in petroleum prices we've seen over the last few years illustrate this. We're not buying any less gas than we were before. Prices have to get ludicrous (like in the 70's) before people start to cut back on something they consider a "necessary luxury". Cigarrette smokers will tell you the same thing.