I highly doubt that math makes sense. Especially for an older home.
But I'm in new construction. Built in 2015, so I think I'm good on seismics.
Insurance quotes rebuilding my older home at 1.1 million due to cost of construction in california. A seismic bolt and brace costs 10k. There is a 70% chance of a M6+ in the next 15 years in my area
You're right that bolt and brace is great.
CA average new construction is $680k. [1]
[1] https://www.costtobuildhouse.com/cost-to-build-a-house-in-ca...