Solid card. You replace it with the first use and a it is a great target when a treachery forces you to discard an upgrade because it's 0 cost. You can have additional copies to maximize your chances of drawing and because you can play them under another's player control in multiplayer.

I almost never play a justice deck without at least one copy of this card. Against villains with plenty of side schemes like Red Skull I'd say it's a no-brainer to have a copy for every single player in your deck (obviously limited by 3). Zero costs make this card additionally attractive, so picking it or not is basically just a question of opportunity costs (and at least right now I don't see 25 better cards in case of heavy-side-scheme-villains).

If you were to ask me what the best aspect was, I would say Leadership.

If you were to ask me what the second best aspect was, I would say Protection.

And yet, if you were to ask me what the best aspect CARD was, I would say Skilled Investigator.

There's no other card in the game that I feel is so much of an auto-include. You should run into side schemes in just about every game. Even without doing anything special, this card will pay for itself. Because of that, it doesn't take the place of anything you would rather play. You aren't sacrificing anything by dropping it down. Normally, the more cards you have, the less consistent your deck is. But if you have a 40-card deck, a copy of Skilled Investigator can only make your deck more efficient and you'd be better off making it a 41-card deck just for this.

This is true if you're doing nothing to play side schemes, but even more true if you have player side schemes in your deck. And since you're playing Justice, you probably should have player side schemes. A lot of player side schemes are good enough to play without Skilled Investigator. Most heroes will have key upgrades that will want Superpower Training. There are tons of incredible support cards you'll want to be able to cheat into play with Build Support. And now we have Run Them to Ground which straight-up skips a whole villain turn.

This was a great card before player side schemes were added to the game, but it's only gotten better since.

I really see little reason not to have a copy of this per player in every Justice deck you play.