A lot of tax "planning" can be divided into two categories:

1)  People do the right thing for the wrong reasons.

Should people save for retirement? Yes.  Should the amount they save be determined by some external incentive, like whether the tax savings is 12% or 22%?  No.  If they ask you, "how much can I contribute to an IRA for a net $5,000 cost?", then the tax bracket is important.  But people who wait until April to contribute to IRA, often pay the 10% penalty for withdrawing it a few years later. 

2) People do stupid things just to save money on taxes. 

The best example of this was back when a tax credit was enacted for solar water heaters.  They were selling for less than $2,000 each, because that was the cost to produce them plus a reasonable profit.  Then with tax credits, people waited in line to pay $3,500 or more, because it was going to save them $1,500 in taxes.  Great for the vendors, and I suppose if it makes people think they have put one over on the government, there's really no harm.