As far as I know my insurance is based on the new value of the machine. My insurance company (Axa) couldn't care less whether I'm running an IMac G5 or a PowerMac dual 2 G5. If they cost the same, they will still be worth the same amount after x years.
And as far as getting the money back for a new machine. It all depends on what kind of insurance you have. I have a policy lined up for when I buy a new Powerbook in Jan./Feb. which'll get me a new machine for the first 3 years, irrespective of what the cause of damage was! And all that for 100 euros per year (assuming a new powerbook will cost me the best part of 3000 euros!) 🙄
I can already sense that my powerbook will mysteriously fall down the stairs when I feel like having a new one... 😀