If you're interested in contemporary art SMoCA is definitely worth the visit but if it's not your cup of tea it might not be worth stopping in since there isn't a whole lot to the museum on a whole. As far as I could tell from my out of town/limited experience, there isn't a large permanent collection but rather a rotating series of exhibits. This means there are a lot of interesting pieces and artists passing through regularly but it's not always reliably solid. If you live in the area it would be worth visiting regularly to keep up with all of their offerings but if you're traveling through, it might not be worth stopping in unless you're REALLY interested in contemporary art or are familiar with in the current exhibit.
Free parking next door and we came on a Saturday when some of the exhibits were in transition so it was free. I think maybe we spent about 20 minutes so it was a quick pop in and out. They also have a cute smaller gift shop with some fun items and accessories as well.