Lindsaybluth, good post. As you mentioned, more money often gets you better anesthetic drugs and better follow-up. Also, depending on the procedure and assuming I had the money, I WOULD consider it worth it to spend more on a vet with higher overhead and more education, because that higher overhead is likely to mean better paid and more experienced staff, and more education and experience with the particular procedure (e.g., complicated orthopedic procedures) means a higher likelihood of having a good outcome.
As for shots and such, some people feel better paying more for vaccinations at the expensive vet because it means that they have an established rapport before they have to use the vet’s more expensive procedures in which the price difference does affect outcome (you’d be hard-pressed to argue that you are getting a better service if the vet charges $40 for a vaccine vs $15 for the same brand). It’s also quite reasonable that some people would rather save money on routine visits so that they have more money to take their dog to a specialty hospital when something serious happens.