Nick,
My deepest condolences on the loss of your gear. It really really sucks that you have to go through this.
It also strikes me as likely that it was an airport employee that stole your gear, since you got your case back. There may be accountablility as to when the cases go missing, but not what is in them. Airport baggage check people have long been rumored to be some of the most thieving people on this Earth.
Based on some personal experience of getting screwed by airlines, I can tell you that nearly all the airlines pay you based on as you have said, a ratio of a fixed sum, multiplied by weight. As such, you would be quite literally better off having them lose a case full of bricks, rather than diamonds.
About 8 years ago I was travelling through Europe and the Middle East, and my tuba was lost on every single flight. Though it was always quickly found, I thought very seriously about shipping my tuba back to the US by UPS, and filling my tuba case with sand to check in for the flight home.
This is absolutely not the time for an "I told you so," but in the future, keep in mind that a pelican case usually is a siren call for thieves; it is almost always an object of value, like cameras, electronics, etc.
And one more important thing for me to add: after a few days of correspondence, you will be very dissatisfied with the result, it is almost inevitable. I would suggest, especially based on the value of what you have lost, that you mention to the airline people that you will be consulting your lawyer, and that they will be hearing from him. Also, I would make sure to actually find a lawyer if you don't have one. It will be important to get your money back. You didn't screw up here....it should not be a foregone conclusion that you will have your things stolen from checked baggage.
