One option before thinking of spacers then if you are running 17's is to go up in diameter and increase wheel width and wrap them with some performance tires. Your handling will be crisper and you can use your 17's for winter driving.

I would try the rims and tires 1st and see how much better it handles. At the end of the day though, you are drivng an SUV/SAV. Adding spacers alone isn't going to make a difference, especially if you have big sidewalls and non performance based tires. Adding rear spacers to your existing set up could potentially even make it worse, it would be less neutral.

Lots of threads here on spacers, tire/wheel combos. Try the search link up top and see what is out there.

Good luck.