Arbitrary caps (or thresholds) usually don't work. Take for instance a similar problem with Obama's mandate on businesses having to insure people working more than 25 hours per week. Okay, well, some businesses just capped workers at less than 25 hours per week.
So if you start talking about adjusting tax brackets, well, people just get to a point where they don't want to increase their productivity because of the increased tax rate. It creates an artificial ceiling.
Best thing to do, in my opinion, is to get rid of the income tax, which is a tax on productivity. Like the old saying, 'A fine is a tax for doing wrong. A tax is a fine for doing well.'