I'd say its worth about what Federal charges for 'em new, I don't know how much they cost new though. I bought a NOS in the Federal box 4 section solid red with clear inside section dome for $50 shipped from a Florida surplus company about three years ago, they could have got more they just wanted it gone.
Considering the AeroDynic is still in production and you can order new domes from FedSig, they would be worth less the 1/2 of new in my opinion. How can you tell how old they are? The domes are very expensive new because they are glues sections and you have to order them by section for the specific lightbar. They are still worth good money, but they are not anything that one can still not get new.