This card is quite bad. It might seem superficially attractive, as it's a skill card you can use to boost any important test, and then maybe get it back to boost another important test later.

The problem is the "succeed by 3 or more" requirement. This means that if you did well enough to get Opportunist back, Opportunist did not make a difference on the test. There are several Rogue cards that care if you succeed by 2 or more (Quick Thinking, Switchblade, .41 Derringer, etc.) but there are none except Opportunist that care if you succeed by 3 or more. So if you play Opportunist and succeed by 3+, then you get it back, but it didn't make any difference. If you succeed by less than 3, maybe it did make a difference, but then you lose Opportunist. See the problem? Even though it looks like you can use this card over and over, it actually can only help you a maximum of once per game, because once it makes a difference, it's discarded.

You might say that the point of Opportunist is that it won't be wasted if you happen to get a really good result, whereas something like Unexpected Courage would be. But in actuality, there are virtually zero tests where a) +1 makes a large difference to your odds of success and b) you nonetheless have decent odds of succeeding by 3+. The math just doesn't work out.

Moreover, there's always a chance that you fail the skill test (or succeed by 1, or succeed by 2 on a skill test that doesn't care how much you succeed by), in which case you lose Opportunist having gotten no benefit at all. Of course, every time you commit any skill card there's a chance it will be wasted. But other skill cards either do more to help you pass the test than Opportunist's rather measly +1, or grant a more useful reward for success.

Quick Thinking is a similar card that is much more useful. It has a better benefit--an extra action is better than just getting Opportunist back in your hand. (Consider that you could use that action to draw a card, or you could use it to fight, move, evade, or whatever's useful at the moment.) Quick Thinking can be used to boost other investigators, whereas Opportunist cannot. Finally, it has a lower activation threshold (2 instead of 3.) Unexpected Courage is a much-superior card, too.

Nonetheless, in the days when the Rogue card pool was thin, Opportunist would see some play, just because the wild icon was helpful. But with a recent influx of quality Rogue cards like Quick Thinking, Think on Your Feet, and Lone Wolf, Rogues no longer need to fill out their decks with chaff like this. Opportunist can be safely set aside.

The Exceptional keyword doubles the printed experience.

Do the investigator's deck building restrictions refer to printed XP or total XP cost?

For example, could Wendy Adams add this card to her deck, as she can only buy rogue cards costing up to 2 XP?

This is quite an interesting card. Note that the triggered ability only requires that you not have resources at that moment; there's no reason you can't use this with Physical Training or Arcane Studies, or even better the permanent Scrapper or Keen Eye. Fire Axe should also work, as you would use the card action, then the free action to convert resources for +. And it's 0XP to boot, so all of the Dunwich investigators can use it, as well as Wendy Adams and Agnes Baker.

I could very easily see this becoming part of my standard kit in many many decks.

With Undimensioned and Unseen, we might have seen the first real target for Mind Wipe. And man is it a big one. Spoilers ahead:

Taking down a Brood of Yog-Sothoth is no easy task. First, you need to find the Esoteric Formula before you can even attack it. Then, you are faced with making a combat check against 6 to damage it - made easier by clues you can put on it, but 6 is nevertheless the highest combat we've seen on an enemy thus far. Even if you succeed, you only deal one damage to it, whereas it has 2-5 health depending on how many investigators you are playing with.

Or, you can skip all that and play Mind Wipe. Better yet, since you are probably playing Agnes Baker anyway and have Forbidden Knowledge, immediately follow up with taking 1 horror using Forbidden Knowledge and kill a house sized invisible monstrosity without breaking a sweat.

Oh, but you don't get its Victory I. But I think that's a fair price to pay for the amount of effort you save.

This Card can be played after Double or Nothing, as it raises the difficulty (if the resulting difficulty is 2 higher than your base value). This card refers to the modified difficulty of a test, not the base value.

With +3 to any test, this is very cost effective solution to resolve Tests, with Double or Nothing, even if another Player uses her Double or Nothing for you.