Just out of curiosity, what would be standard upkeep and updates for a home built in 1965?

My concern is centered around bathrooms, paneling (walls) as well as furnaces and a/c units. I'm interested in a home (3000sqft) that has neglected to update any of these items, so they are all original. Some of the elements of the bathrooms (4 full in total) have been mentioned to have been having small problems and honestly the originality isn't in the realm of 'vintage'. The reason I ask is that the owners believe that there home should be priced as an 'average' home and is utilizing an average price/sqft to base their price on.

Any feedback on this question would be much appreciated.

Thank you much