That used to be old times.... They were deemed rare and were wroth upwards up to several million gold even though the trade price was 50k. Jagex has resolved this and the only use for it is the 100% energy restore it provides
They will never be rare anymore since of the update that made you get alot more mint cakes from the gnome cuisine minigame. I did it right after update for an hour and managed to get 2.5m worth of cakes
They have dropped alot since then though.
Nothing is special about them any more.... that was about 2 months ago, and they were a popular item involved with junk trading, going for a LOT more in street price than their actual value.