At first glance it looks like Spirit is using a tiny fraction of their new tax savings to give you guys a minuscule increase in compensation.
I'm sure someone will come along soon and run the numbers but the run rate of your new contract ought to account for the companies huge windfall due to the tax relief.
Don't be afraid to vote no, the sun will continue to rise each morning. Delta and SWA both voted down the first TA and have much higher rates and are both printing cash. Good luck!