There are a number of reasons to visit SMoCA. I'm not a big contemporary art fan but I find it interesting and it's worth a trip every so often to see new exhibits at the museum.
My #1 reason for visiting SMoCA is to hang out in Knight Rise, a skyspace by James Turrell. It's an elliptical room with a 10'x15' eye like opening in the ceiling. As you look up you feel like you can touch the sky; it's an experience that can't be missed.
Tip: Go about 15-20 minutes before sunset and stay until 15-20 minutes after sunset.