The 457 plan is a wonderful tool. You do NOT have to wait until age 59 1/2 to withdraw from it. It is simply "deferred compensation," so once you leave the job, you can pull money out and only pay income tax on what is distributed. You also have the option of rolling the money into an IRA when you leave, although you lose the early withdrawal feature if you do that.
If you contribute to the 457 plan, you can use the investments as part or all of your pre-age 59 1/2 FIRE income stream. Maxing that plan out can bridge the income gap for many early retirees.
Yes, you can contribute the maximum amount to BOTH plans, which for 2012 is $17,000 each if you are under 50. Go for it!