My understanding is that if your policy is for replacement value, you base the insured value on a similar item available today. I would consult your insurance broker to make sure, since that is his/her job.
+1...My house got hit by a tornado in 2008. The insurance company paid out almost $100,000 for just my high-end audio/video gear.
Thank goodness the tornado hit opposite from my record rooms. That would have been awful and VERY sad.