To help people that are new to the game get accustomed quickly, you could give a slight bonus in shards to lower level players, eg
Level 1 : 50% bonus
Level 2-3 : 40% bonus
Level 3-5 : 30% bonus
Level 6-9 : 20% bonus
Level 10-14 : 10% bonus
Level 15-20 : 5% bonus
Level >20 : 0% bonus
Sound good?