The shim plates are almost necessary for CB's because otherwise the 'beater rails wear grooves into the shoes and the connection becomes sloppy with lots of vertical play even after cleat replacement. Nice to hear about the multiple shoe lifespan. This kind of wear isn't as much of an issue with SPD from my experience.
I'm interested in what kind of maintenance regime and lifespan Andrew gets out of his pedals. Every time they come out with a new version they are like "trust us, these ones are better than the last ones, we swear!" Do you have to buy more than the base model? When I was running CB's, I had to bin the set ($50) every year whereas I've had SPD's 520's (also $50) that I've used with 0 maintenance for 7 years now.