At least in the Helsinki Metropolitan Area, a comprehensive MEP (HVAC and electrical) renovation often costs between €1,000 and €1,500/m2. Surprisingly—depending on the location, of course—sometimes less than half of this is reflected in the market value. Unfortunately, I don’t have any hard data to support this claim, so take it with a grain of salt.
In my own housing company, the cost of the MEP renovation was €1,200/m2, and the estimated increase in value after a couple of years is €600/m2. Of course, the general market situation has also influenced this equation.