A much more relaxed approach would be to introduce an insurance condition as follows:
Any wiring must be up to the electric code in effect when the wiring was done. If the wiring is older than 50 years, it must be up to a code that was in effect no more than 50 ago. Wiring should be inspected and tested every 25 years. The cost for this should be covered by the insurance.
This would gradually force the very oldest of wiring to be upgraded. As upgrading means new work, the latest code apply. The periodic inspections will catch the work of handymen/D-I-Y and cowboy electricans that tend to accumulate over the years.
[This message has been edited by C-H (edited 10-07-2005).]
