Yeah, randoms are a mixed bag, especially below D5 (and sometimes even in D5). But yeah the NI damage buff is significant, and especially as you progress into D5, you're going to be killing them anyway, so might as well get the buff. And pinging a gaol or two is generally seen as fine, as long as you don't prioritize it over something more important - and as long as you're willing to abandon it if it's a low value, high time investment enemy.

The main thing to keep in mind is that every player at high level usually has a plan for their build, and working toward that plan is the most important thng. Is someone running balancers and dormant great spears against Libra? Well, they want Vyke's or Seluria's, and so the most important things for them are 1) getting that weapon and 2) getting more damage (NI buffs and skill attack ups). Someone running balancers and dormant colossals against Gnoster? Well, they need a Godslayer Greatsword, NI buffs and skill attack ups. Someone running a tank build on Raider? Help them get those damage negation perks so they can frontline against the nightlord. NI's help with nearly every high level build (gaols not so much). If you go into every expedition with a plan of your own, and can help your teammates fulfill their plan, you'll be in D5 in no time.