Do higher efficiency gas boilers cost more for repair parts and do they have more parts?

My parents had a newer boiler than mine. When they had a gas valve replaced, it cost nearly $500. I called a different HVAC company and they said that it was about right. I am trying ess the wisdom of buying a new boiler. I have an old Maclean-Weil (hope that's right) about 40 years old for a split level home about 1800 square feet plus sub-basement.