It's not all about what parts are changed, a minor service will only include checks on some of the parts, so you would be better off negotiating a price for a major service, less the air filter and plugs.
A major service will be more thorough and should include jobs like stripping and cleaning the brakes etc. I think that once a car gets beyond 3-4 years old, it needs more regular checks as opposed to simply swapping fluids and filters.