Most bags have an upward liability limit of around $3500 per ticketed customer so you can get reimbursed for items bought above $500 but you have to deal with the claims dept. in the airline. It is much easier to just take the $500, all most airline reps will do is verify that they saw a receipt and mark the case as settled for $nn.nn amount.
Separate pro tip: if you ever have any issues, like any issues at all, on a flight, stop by the airline office and just say that you had xyz difficulties and that you normally enjoy flying with said airline and is there anything they can do to make the next trip better.
9/10 times they will give you vouchers for various items available on the plane.