And then - this is the most important part - Larian has the game follow up on the threat - just a bit, though. Just enough to remind players that "Hey. You might not want to just spam long rest." After 2 long rests from the time you landed on the beach, you have your first Dream Lover sequence. Boom. Right there. If you know that you're going to have a Dream Lover sequence potentially at any point when you Long Rest, HECK YEAH, most players are going to associate that with the tadpole and think, "Dang! The more I long rest, the more likely I will have one of these weird Dream Lover sequences. I'd best avoid long resting if I can help it." And if the player is all into the Dream Lover, then they will long rest more which is totally fine at that point. Let them. Then they can embrace the Dream Lover.
And I'm not talking every 2 long rests. I'm just saying that maybe the first one is after 2 long rests. The next Dream Lover dream could be 8 long rests later, or something like that. It would be like a reminder. "Hey. Keep long resting and you'll get more of me, your Dream Lover." The next dream could be 10 long rests later, or if you use your tadpole powers, it comes sooner. Whatever. The point is that they could EASILY use this system to dissuade Long Rest spamming, it wouldn't be a hard time limit at all, you'd actually eventually get to see the Dream Lover sequences even if you aren't using tadpole powers, and so forth.
That, to me, is a MUCH better system for "limiting" long rests than camping supplies and such. You wouldn't even need to do other consequences but the dream lover to discourage long rest spamming. I still think other consequences, like Lae'zel leaving temporarily, make sense and would be fun and provide even more replayability to the game, but at the very least the dream lover being a consequence would make sense, and it would work to deter people more. Especially after the second or third dream where the party starts to show signs of transformations, and you are given even more illithid powers. Yeah. I think players would be a bit less long rest spam happy if they thought, "Holy crap! We're transforming into mind flayers!" Even if they aren't.
Unfortunately I have to disagree due to established story reasons.
The tadpole itself is dormant and in Netherese stasis. Time does not make it any more powerful exactly because of this stasis. This is established by Halsin, hinted by Nettie and outright confirmed by Omeluum (who even gives you a ring to forcefully discourage you from making it more powerful). And we have other True Souls who are living proof of that. So by making dreams appear after X amount of long rests regardless of whether or not we use the tadpole would heavily contradict the story and the tadpole's existence.
Contrary to the party's belief who don't know better yet, we are under no danger from the passage of time whatsoever due to story reasons established.
So once again it is important to add; unless the story is completely cut off from the mechanic, trying to discourage long resting is a big NO from me. Instead they need to implement it better so that it feels cohesive with the story and events within it.