Got the 15mm spacers installed on the front and back. Looks and drives great. Not sure if I'm imagining it or not, but it feels to me like the steering wheel is a tad lighter and the springs a tad softer. Took it up to highway speeds and didn't feel any weird vibrations. The car still feels very stable at high speed in a straight line. Haven't had a chance to take it onto twisty roads so I don't know if there's a difference there.
That extra hole I was asking about on the Eibach spacers didn't line up with anything on the rotors.
I took off the 5mm spacers that were on the car. It had two tapered bolts to fasten it to the rotor. Once the 5mm spacer was removed I saw two tapered holes on the rotor that looked like they were designed just for keeping those tapered bolts. The mechanic at the tire shop suggested I put the tapered bolts there. Is that a good/bad idea? Is that what its for? Unfortunately I forgot to take a picture of the rotor with the wheels and spacers off.