Very very good question Larry,
And soooo many variables.
All kinds of things like electric v/s mechanical heads, almost no electronic v/s lots, cheap effective bottom paint v/s very expensive so so paint and electronic mini furnaces v/s oil stove heaters.
As to the question probably not much difference. Things costing more for old boats ballanced by things costing less on newer boats and the other way around. And complicated expensive things that cost a lot not even present on older boats. Regular oil based paint much improved but all new two part coatings as well. Boats are much like cars too. Newer cars much more complicated and expensive to repair when something goes wrong but much less goes wrong. Same w boats.
For all except navigational electronics much of the old boat and new boat comparison finds them more the same than different.
I don't know if newer boats or older boats cost more to maintain. It's hard to compare the boats w/o considering the huge difference in fuel and moorage costs. But if costs were compared adjusting the dollar value to hours worked at the different times to show how many working hours would be required for X amount of maintance ....... then we't know much better.