Any exhaust system modification that changes the location of the O2 sensors is illegal. Long tubes will require changing O2 sensor location. Depending on the type of emissions testing you have where you live, can make a difference as to whether it should concern you or not.
Your car (profile says 3.5) is not a big torque producer. If your goal is to increase performance, adding long tubes can help on the top end with horse power, but not so much where the 3.5 can really use a bump.....Low end (acceleration) torque. IMO, short headers can give you more of what you can use.