I performed at the festival a few times in the late 70s, early 80s, but it got to be too much of a mob scene for me, and I don't generally attend that often anymore. The organizers' idea of "folk" seems to be "anything that folks do." You're just as liable—more liable, in fact—to hear a bunch of grunge rock garage bands as you are singers of traditional songs and ballads. As Forrest Gump said about life, the Northwest Folklife Festivals are "like a box of chocolates. You never know what you're gonna get." If you actually want to hear some traditional music, it is usually there, crammed up in the northwest corner of the Center grounds somewhere, but you have to either know, or get a program ahead of time and study it carefully to see who's going to be there and when and where they'll be performing.
I do go if there is someone special that I want to hear, or, of course, if I'm performing myself, such as at the 2003 "Coffeehouse Reunion Concert" (Geezers' Concert) and/or participating in a workshop. I'll be there this time around for the Seattle folk music history workshop.
The Seattle area, and the Pacific Northwest in general, has a pretty rich folk heritage, and there was a lot of activity here well before the popular folk music revival of the late 50s, early 60s.