Around here (Ontario) I can't even get comprehensive/collision coverage on a bike as old as my '78 until I'm 30, at which point I can get classic insurance, which is only offered by ONE company.
For classic insurance, you get an appraisal every 2 years to get coverage. I wondered about this too though, because even when I can get classic insurance, will the appraiser put the value at what kinda-sorta restored bikes are going for around here (which doesn't reflect my effort, but I didn't go all the way -- there are still some scratches on the chrome bits because I didn't replace them) or what a top-to-bottom resto costs?
I plan on telling the appraiser what everything cost -- paint job, pipes, seat, engine work, literally every maintenance/rubber item, etc., and hoping he agrees.