I believed this was a great card. I made the huge mistake to use it instead of Unexpected Courage

Location with clues are indeed plenty during the game, but what is the purpose of the Seeker class ? Empty them. And when it's empty, this card is a dead weight in your hand. You'll have to pay attention not to end your turn on an empty location, which requires too much planning and is often counter productive

Unexpected Courage will be enough in 80% of times, while half the time, Inquiring Mind will be completely useless, often at the wrost moment (Encounter deck draw)

Maybe in addition to 2 copies of Unexpected Courage, but even then, I'm not convinced.

A card that is as strong as it is simple. Most locations in this game have clues on them, and you will be doing plenty of skill tests on such locations. Inquiring Mind's three wild icons and ability to boost any investigator (unlike, say, Rise to the Occasion) provides a lot of flexibility to the team. Whatever the situation is, as long as there's a clue in the area, Inquiring Mind will be a significant help. It can give almost any investigator at least a half-decent shot at doing most things, even on Expert, and that's pretty nice.

Although it is a virtual certainty that, no matter the scenario, you or your teammates are going to take multiple important tests on locations with clues, this card does occasionally peter out late in scenarios when all the clues are gone. Usually you can tell if this is about to happen, and thus commit Inquiring Mind to a test before it deactivates.

If you draw Inquiring Mind after all the clues are gone, it probably won't be very good. But this is going to be pretty uncommon, and in any case this is true of a large number of excellent Seeker cards. I don't consider this a major strike against it.

I suppose there is some synergy here with the Seeker cards that let you drop a clue on your location (Forewarned, Dr. William T. Maleson), but this is probably not a big factor. You don't need to run these cards for Inquiring Mind to be good.

I think I slightly prefer the upside of Inquiring Mind to the reliability of Unexpected Courage, though I don't feel strongly about this. The difficulty level may be a factor here--the higher the difficulty, the more useful Inquiring Mind's third icon will be. Which card is superior is a bit of an academic question, however, because I often just run both in Seeker decks.

As useful as this card is, +3 to a skill test is not quite so powerful that I would use a splash slot on it. There are many higher-impact choices out there. (For instance, if you're looking for a general utility card to help you pass skill tests, Lucky! will be the stronger pick.) It may find itself on the cutting floor as XP cards come in. (But not in Minh Thi Phan; she will most certainly want to run this all campaign long.)