Primary Spending for laurels should always be in your tech upgrades.
Never use laurels to fast track your heroes, that's what transcendence is for. If you aren't at a point in the game where you can get transcendence, wait - you need the laurels in your tech.
Farm/Area/Mine/League Battles -
Depends. My take on this is if you are over flowing with excess spend away. If you aren't, consider only doing 5 inspirations to get a single bonus like 10% dam.