I see your point but we are in our 40s
and this is the forever home so not too fussed about future sale value.
Sorry, Mark, but someone in their 40's has a long way to go (hopefully). There is a lot of water to go under the bridge, and life rarely pans out as you expect (that is from personal experience).
The heating is part of the house, and should be designed as such.
I did not see where you said the heating circuit is 10mm, but if it is, and you are totally refurbing, then definitely repipe.