Probably depends on what you’re doing. I know I targeted conduct wq rewards on alts because I knew I’d need them, but I didn’t go after any of the havoc ones on my DH, so I guess I could maybe fill out the tree with the jank general ones.
Weapons and trinkets are usually my issue, but I stopped switching specs myself in BFA.
Maybe! I just did them all, because I knew they weren’t going to stop giving them to me, instead of anima. So I just nabbed 'em all. Kinda like Pokemon. 
Trinkets I never had an issue with, because I’d get generic intellect ones. Caster/healer was easier, because same weapons. I hate Paladin, now, so I only had to fuss with weapons for WW. Which was easy at the end of the campaign, because they handed me a 187. And turning in the ToF zone quests got me weapons.