I was reading another thread where I asked something similar, but for shard farming is there even really a point to level all the way to 50?
At level 20 botanist and miner gains Ward Skills, ward skills are crossclass so you can use them with miner and botanist. If you only want to farm shards you don't need anything else but at lvl 41 and 50 you will gain a trait to extend this skills to crystals and clusters.
Are crystals and clusters only farmable in the higher zones?
crystals are lvl 20+ nodes iirc and clusters are unspoiled lvl 50 or whatever they are