This is sorta part of what I do on a daily basis. Dealing with antique collectors, insurance questions pop up all the time.
I started collecting with a group of 19th and early 20th century handbags. I insured those puppies, no hesitation at all. I had them appraised and put on a rider to my regular insurance policy. If I had multiple new bags, a new, harder to find Birkin, or an Hermes with exotic skins, or a vintage Sac a Mallette (did I butcher that spelling?) I would probably insure a bag like that.
From my past experiences, I would think that the problem with insuring a bag like a single new Birkin as a rider would be that the insurance companies frequently charge a high enough fee that you could easily buy another handbag relatively quickly if you put that money in a savings account and didn't touch it.
Insuring vs. Not Insuring. It's a gamble.
I don't know if this helped. Hope I didn't ramble too much.