It is a bit expensive to put in, so I wouldn't do it unless you plan to live there long enough to recoup the costs. If I were to sell my house nobody would give me a dime extra for it.
It was eye opening. I got a taste of exactly why builders build crap homes. Building code is the minimum and they build to it for a reason.
We are now friends with the people who bought it and several times they have thanked us for building it well. They didn't know what they were getting, but it is nice to see they appreciate it now - especially when the power is out and neighbors are crying about their cold houses and these lucky people are staying warm.
My third and final build I built for me. I never plan to sell. Even when my kids are gone and I only need half the house it would be very hard to find something to downsize to that would cost me less per month than I pay now. Ground source is that good.
Do you think this is really an information asymmetry problem? What if there was a standardized way to compare the cost of maintenance per M2?
Anecdotally it doesnt seem to have a huge impact on the asking price.
My house is from 1935 and the statistics tell me that it is practically impossible for me to get the house above C. I think that it is theoretically possible but the required investment will be so big that it makes more economic sense to tear the house down and build it with modern materials and techniques.
https://sparenergi.dk/forbruger/vaerktoejer/find-statistik-p...
[0] https://energysavingtrust.org.uk/advice/guide-to-energy-perf...
Of course, most people haven't cared that much about it. But it's changing with higher energy prices. I had a friend regretting buying something with grade F, for same square meters he pays like 10x the amount for heating than I do in my C apartment. (scale from A..G)