The Vatican's most valuable holdings, Saint Peter's Basilica, the Sistine Chapel and the Vatican Museums' collections, are inalienable and never appraised for sale, so there is nothing to price against a market the way an ordinary asset is valued. The Holy See's own financial disclosures (APSA's patrimony report, the Secretariat for the Economy's consolidated statement, the IOR's own report) each cover a defined administrative scope and none of them attempts a valuation of the art or the buildings themselves.
What would resolve this There is no method that would settle this honestly, since a genuine market valuation would require a willingness to sell that the Holy See has never expressed and that the objects' religious and cultural status makes very unlikely ever to exist. What would change the picture is not a single figure but a named methodology the Holy See itself adopted and published for insurance or heritage purposes, stating clearly that it is not a sale value.
OpenCultural heritage economics and museum insurance valuation practice, in dialogue with the Holy See's own financial administration.How Much Money Does the Catholic Church Have?