Takashimaya in Shinjuku has a store for music / video / computing products. I wouldn't expect them to have the best prices, but it's probably a better deal than taking your vouchers to one of the ticket stores, where they'll probably buy them at 20% off face value or something.

I was about to offer to buy your vouchers from you - but I asked Mrs. Jib if she needed any depato vouchers, and she says that there's nothing she wants to buy right now. This is a rare event that deserves to be marked in some way... I'm going to put out the flags. (Look out for them all over town in the next couple of days).