Seems like a good idea John. Better safe than sorry. Most insurance companies will use a book value that likely doesn't include upgrades. You can keep receipts for work done but insurance companies will likely call this maintenance and not want to include these amounts. If you do it yourself you have no receipts and insurance companies aren't likely to consider your labor. An appraisal, from a recognized appraiser, solves the question as to the value of your unit. I suggest you advise your insurance company of your appraisal. They may take issue with the amount and you need to be aware of this BEFORE you are in a position to make a claim. Insurance policy particulars can vary greatly. Ask about a 'total write off" and if there are limits involved, deductibles etc.
I learned about these things some years ago when I had a total write off of a five year old unit. "Replacement cost" would have been purchase price minus depreciation, as calculated by the insurance company. "Guaranteed replacement cost" is purchase price of a NEW unit, of similar size and with similar options but no depreciation. HUGE difference.
Also, more coverage usually equates with higher premiums. How much coverage do you want and what are you willing to pay for it?