The price of parts does not seem to be decreasing in line with bike values.
I am not surprised, as everything is affected by wages, energy, rates etc.
However, it does make it difficult to justify the spend on restoring a bike when the parts and services ie painting, wheel building are likely to cost more than the bike is worth.
The value of parts does depend on demand and bike they fit.
A similar Honda Cub part is clearly not going to command same price as a CB750 K0 or for a Vincent

I have been put off restoring bikes I have been offered and I am sure may others are.
It was generally about the challenge of bringing something back to life.
I always knew I would not make money, but you do hope you are not losing too much.
An inexperienced restorer will probably be shocked at actual cost and disappointed.
As a friend said, "any hobby costs money"

but it does affect my motivation.
I guess that vendors will lower margins if demand drops and there will not be the financial return to remake parts.
Probably more bikes will be broken as worth more for parts

Interesting times