I finally researched insurance for instruments. My insurance company covers such under a "Valuable Personal Property" rider. The difference from household/renter's insurance is there is no deductible, coverage is for full replacement, and coverage includes loss and theft. Or so it goes for my company. Total annual premium for the $5000 value I placed on my two guitars is $13.00.

Now...my company is widely known for its excellent service and lower costs, YMMV with your company. Still, the premium cost can't be hugely different between companies. Additional rider protection for our instruments looks like a deal!

(this is for "personal" property, the VPP rider does not cover instruments used professionally)