I take tax-rates much more seriously. Taxes are a direct line to slavery--obviously a 100% tax rate would be complete slavery. My current 1/3 tax rate makes me 1/3 slave--maybe a fair trade for being 2/3 free, but a trade nonetheless. Unfortunately, as you succinctly pointed out, tax rates of late have had little relation to spending, but in the long-term input = output, so as a young individual I see taxes and spending as two sides of the same coin.
To the extent our government has shown restraint, I think that is due to people making their concerns known and visible, as well as some good old fashioned American luck. Politicians will tend to acquire as much power as the people let them.