BLM and SAM shouldn't get utility, as it would be balanced with a potency nerf.

What they could get however is some kind of selfish symbiosis, ideally one that's not directly potency related.

For example:
Tributary Lines (level 60-70 blm trait)
Each party member who stands within your Ley Lines grants themselves and you a 2% spell speed increase.

This would also indirectly encourage caster/ranged parties as they could stack in the BLM Ley Lines and increase the BLM damage, sort of like increasing their own rDPS.