Do you mean economically? Insulation is absolutely sensible ecologically, it saves the multiple of the oil used. I have something like 10-20 times in mind, but don't hold me to the exact number.
The energy payback time depends on the material and is probably somewhere between 0.5 and 3 years, depending on the material and application. I have just insulated the facade of our house myself and my name is not Konrad Fischer either.
A renovation obligation would not exactly increase the willingness to renovate buildings in many cases, but on the contrary give momentum to the skeptics and punish those who have no reserves for this or do not have the income.
Because despite energy payback, the monetary payback time in years is usually double-digit, if it can be realistically achieved at all.
What are the current construction costs in the area of ETICS installation (in existing buildings)? I still have €150/m² gross in mind – 2020.