The last time I attended a gun show in Hillsboro (four years ago) it was a complete waste of time. One room at the Fair Grounds. No local shops, just guys selling parts and old beat up guns.
Well, I was pretty sure I would go being it's so close now I'm not so sure seems anyone who has been hasn't had a good experience.
Free parking and cheap entry fee. Go late and you get a free pass for the next show you go to. Look around until you've seen all there is to see, usually not too long. Use free pass at the Portland show.