How much you insure it for may depend on the type of insurance you are getting. I have my basses and rig insured for what it would cost me to replace them. For instance, I had my F-1X preamp insured for around $400 for a while since that's what they were trading for on Ebay. When the going price for a used F-1X went up to $500, I increased the insurance value to $500. So, for me, I would insure it for what it would cost me to get another one. If you wanted to insure it for what it would cost to get a new one, you could probably do that as well, though it would probably cost you more to do so. Again, it depends on the insurance agent you are dealing with and the type of policy you are talking about. Since I gig with my basses and rig, I have a commercial policy. So if I had a nice five string Orion with case and I thought it would cost me say $1,500 to replace it with one in similar condition, then I would add it to my policy at a value of $1,500. You may want to run a search on this site for insurance since this topic has been discussed several times and a number of people have made some very informative posts on the subject.
