The ohm test is conclusive. Like you said, if the resistor pack is bad it will be pretty obvious - those coils will be visibly burned out. I don't think that the fan motor runs on two circuits either. I'd suspect the switch just like you do. I can drop some spares in with your wiper set. Just mail them back once you solve the problem.
You know, there is an odd little safety switch on pg 522 of the Bentley. I figured it was a straight through contact from fan speed 4 on the switch to the blower motor. Hmmm. I'll see if I can dig anything up about that.