That is true Splinterlands is almost a Blockchain unto itself. The market will soon be flooded with cards. I also hear a lot of more advanced players say they are leveling up certain cards as fast as they can. That will in turn also remove cards from the market adding to the value of the card.
There are a few strong cards that are almost a no-brainer to level up fast. I am holding off a little for a few weeks, but only because I am planning on buying a few thousand more packs :)