Since every league has it's own pool, your absolute reward shares aren't important. What is more important is the number or reward shares you earn relative to all other players in gold.

If everyone in gold feels the same as you (it's not worth it to buy more copies of those cards, then your rewards won't be affected.

The question becomes, do you have a more leveled up deck than most people in your league? If yes, then this may lower your reward shares but increase your earnings.