There are two techniques that can go 90% of the way to making playing-initiated retreats like this not boring or tedious.
Use your role as DM to control the passage of time. Skip the uneventful parts. Do you know that nothing will inconvenience them on the way out of the dungeon? Narrate to skip ahead then.
You backtrack through the halls to your camp hidden outside the dungeon. Two hours of walking and resting later you're rested and ready to head back in. What do you want to do?
This is part of a family of techniques called scene framing, because you're skipping ahead and then reframing the situation the players are to make decisions in. There's no need to have them decide and describe their every twist and turn as they backtrack out of the dungeon; "we leave the dungeon" is plenty. (Having them walk square-by-square on a battlemat would definitely be unnecessary and tedious!)
No need, of course, unless there is…
The world doesn't always stand still
Sometimes, skipping right back to camp can itself be boring. There's nothing more of an adventure-mood killer than knowing you can traipse around completely safely. And what's more, there's never any justification for acting like dungeons and wilderness are completely safe — they never are.
So ask yourself, "Does anything happen meanwhile?" Think offscreen, and think about what the dungeon denizens are up to while the PCs are letting off the pressure. Are they regrouping? Retrenching? Reinforcing? Wandering? Sometimes they'll be sitting tight and cowering, or be unaware of the breach of their outer defenses, so "Hm, no, nothing happens meanwhile" is a totally valid answer. But don't let it be the only answer you ever give. Make things happen that are logical consequences of the larger situation while the PCs are choosing to not push forward. The dungeon becomes a living, breathing place that changes in smaller and larger ways while the PCs are away.
Sometimes, these happenings will find the PCs too, and then their "rest" becomes very much not boring. Players who know that they need to keep an eye out, and watch their backs, make for smarter PCs that are better at surviving than PCs run by players who think they can let their guard down because they "paused" the adventure. There is no pause button!
You can use this naturally in combination with the pacing advice above — when nothing happens, skip to the next point of decision for the players, but when something else does happen, skip right to that event's location and time and start describing the PCs' situation to the players.
It's all about time
So make sure that you skip the time where nothing happens, and make sure that when things happen isn't 100% predictable by the players. These two techniques — one a narrative techniques, the other a structural technique — go a very long way to making rests non-tedious.
Critically, this combination of techniques remove the tedium without preventing the players from thinking smart like they have been. Even better than not preventing them, it actually gives them more things to think strategically about, making the game more nuanced and engaging for strategically-minded players like it seems you have.