Yes, it is difficult and I don't think it is possible to come up with a solution that fits all. What limited I can say: Insurance for the PV is cheaper than insurance for the insulation. That is because more problems with insulation can appear (e.g. fire damage, moisture) than with PV. Insulation of old houses is also far more complex than PV (someone pointed that our here).

.. it was mentioned somewhere here, too: For some, the best solution will be to focus on reducing energy consumption; for other, the better option will be to focus on increasing local energy production. And a combination of both might be best for most.