Ha, those hubs are definitely clean enough! Also, not enough can be said for a quality spacer, since you didn't mention the brand I'm not sure if this may be part of the problem.
Also, I think you know the answer that we're gonna say. Take off the spacers, drive the car at 100-130kmh and see if the same wobble is there. If it is, your tires probably need balanced. If its not there, toss on the spacers when you get home, drive the car to 100-130kmh and if the shimmy is still there, something is up with your spacers.
Not really many other ways to diagnose the problem. I have 10mm front and 15 rear and they all fit pretty snug. Be sure to use some anti-seize or it may be a bitch to get off one day down the road.