You can incur "maintenance debt" like anywhere else and some cans kicked down the road end up not needing to be done or being done in a different/better way. But as someone who lives in an old house, you do need to keep up to some degree especially with things that are only going to get worse if left alone.

I agree the parent lifetimes are probably a bit low. But the basic point that annual costs for a house/property are significant even if you can trim a bit at the margins.

I agree you have to think about it, but things like appliances generally don't cost more to replace if you wait. If you have leaky roof or a wet basement take care of it as it will be cheaper to do now but those types of things don't make up the bulk of the maintenance costs, it's mostly little stuff that you can let slide if you need to. Other things like pest control you can do yourself with a little reading and call someone if it gets out of hand.

My point is mainly maintenance costs are a lot more flexible than rent. You don't fix a washing machine, you won't have a washing machine. Don't pay the rent and your out on the street.

Your old furnace may well be costing you more in fuel than the cost of replacement. A 1980s furnace is likely well under 60% efficient, plus it drafts inside air up the flue. A new furnace will be 90%+ efficient and the firebox will use outside air.

My house is under 1200 sqft and at night in winter we turn the heat down real low and just use space heaters in the bedrooms to take the chill off. We also got new, high end windows in the bedrooms so the space heaters run for about 15 minutes total. Also I like to sleep cold. Payback time is something like 10 - 15 years if it was twice as efficient given the math I did. Instead of a heater I got the basement redone as that was becoming a issue.

Part of me is also sort of thinking that each year I wait the heater I will get in the future will be a little more efficient. I've been thinking about replacing it since I moved in but just recently I'm hearing people in my area talking about heat pumps so I might see if I can give it another year or two and see if that becomes more mainstream and go that way.