The problem with that approach (such as it is a problem) is that it forces a consideration of environmental minutiae that I simply have no desire to bring into a game. Which, of course, is why I don't use things like mimics, or cloakers, or any other kind of "player wasn't being suitably paranoid" encounter. For my desires in a RPG, making the players paranoid sucks. Just give me a number that tells me who surprises who, thanks.
Yeah over-paranoia sucks. That's why there's a concrete
cost to being paranoid: you are performing an action and consuming a limited resource (time, at least, which translates into rations and GP at least). It becomes a calculation: is it worth that cost to be that paranoid? If folks are being overly paranoid, the cost isn't high enough: increase the cost. Alternately, decrease the reward: if something hiding in the shadows can kill a PC in one blow, there's significant incentive to be paranoid, too. If the result is less binary, perhaps the calculation is different.
Why don't you pick all the flowers in the game of
Skyrim? Well, there's a cost. Encumbrance. Time. Marginal usefulness.
Why don't you open all the trashcans in
BioShock? Well, they don't have that much useful in them, and maybe you don't want to spend your time that way.
Why don't you cut all the long grass and bushes in
The Legend of Zelda? Again, it doesn't give you much, and it takes a while. Generally not worth it.
These are all economic calculations, risk vs. reward, cost vs. benefit. You get the economy right, and players will weigh spending that time securing an area vs. spending that time going into new areas.
The paranoid party is, in part, a symptom of a low cost to paranoia (no significant long-term rationing), and big reward for it (you might uncover a creature that would've KILLED you!). Eliminating that paranoia is just a matter of getting the economics right (it's not the end of a character if you don't notice X, and trying to notice X is going to eat up something precious).
You could also play a game without hidden enemies or deceitful characters or mimics or whatnot. They're all really shades of the same thing, and it's fine to not have any hidden info that the players need to work to discover. It sounds like ignoring a big part of what makes adventures dangerous and risky to me, but I've never been too burned by overly inquisitive parties, so I'm speaking from a place of privilege.
More than not hitting a downside, though, I do like it when players engage with the world, especially if they're doing it essentially "in character" like this. In a world with halfling assassins and cloakers and mimics and liars and pretenders and doppelgangers and glamours and illusions being a little cautious where relevant should be a character trait for most successful adventurers. Forcing players to spend a resource to be cautious makes it a trade-off.