Is a 529 a good short-term savings vehicle for my own educational expenses?

If your state's plan offers a good tax deduction and a fixed option, you may benefit a little from using the 529 plan. Unfortunately, most 529 plans rely too heavily on risky investments, so check your plan options for a fixed account and the interest rate.

Otherwise, 2-4 years isn't going to provide much tax benefit on the gain side. Your gain is likely to be relatively small.

On your Roth IRA comment, I believe you are referring to the 5 year window for avoiding the 10% penalty. Qualified education expenses are an exception to the penalty. For unqualified expenses, you can always withdraw your contributions to a Roth IRA without penalty.