Quite a few people have wanted a decrease in cost because they think the ability is a negative one.
A card is underpowered if it cannot be worth using when it is being used at its fullest potential. Would shriekers be underpowered because the AI always burrows them? Are forest spirits underpowered because newbs use them in mono life? No, and no because those cards were not used to their fullest potential. The Ghost of the Past is a strong card when used at its fullest potential, a deck with nightmare.
So yes, this card is probably not worth using unless you have nightmare. However, many other cards are not useful unless paired with another card. Think scorpions + buff, photon + immolation, voodoo doll + ragepot/GP, etc.