Do you currently itemize deductions? If so, recalculate your tax burden without taking those deductions into account except for your mortgage. Would you still save the same? You can't just take your AGI from your last 1040 and change the rates, because the rates would be applied against a different, higher amount after removing the deductions.
A lot of us don’t have any deductions. A consistent marginal tax rate is fair. (The one year we did have deductions we got slammed by the AMT so that sucked.)