If you want to get the 7,500 gold amulet (plus some EXP and other loot) off of the Nabasu in Market Square you have to plan out limited rests up to lvl 5 or so.
You don't. First of all, you can rest as much as you want in the maze without triggering the tavern attack. To get that amulet all you have to do is defend the tavern and then you can go fight the Nabasu. You only miss the amulet, if you skip the tavern defense which is done by those who avoid resting as much as possible, not by those who spam rest. Hitting all the content that gets changed after the tavern attack is very easy, because you don't have to actually do a lot of combat and can do all of it without resting above-ground: clear the tower of Estrod (the biggest part), activate the bridge in the market square, recruit Ember, solve the Hulrun/Ramien conflict (can be done non-violently), free the Flaming Lance Crusaders in the Library (can be done non-violently), recruit Woljif and maybe talk to the thieflings in the market square. After you've done this, you can rest until the tavern defense prompt, defend the tavern, then hit all other content while resting as much as you want. Essentially, there is zero need to ration your rests in the prologue and chapter 1, if you do things right.
If you rest in Gray Garrison you lose the perma-haste.
First of all, having that 1h30min Haste will reduce your need to rest. Secondly, even if you lose the ritual Haste, you can cast it from your full arcane caster while restoring lower level spellslots that can be used for offense (Grease, Glitterdust). Gray Garrison has at least 2 corruption-removing interactions so you can rest there quite a few times, allowing you to drop an AoE disabling spell almost every encounter.
You *can* go back for multiple trips on Leper's Smile and Lost Chapel but most don't.
Doesn't matter what most do or don't, the possibility is there with no real consequences for doing so. The generic cloak/ring you get for the efficient capture of Drezen are inconsequential.
with corruption turned back on rest management is *very* relevant trying to clear it on Unfair
Drezen has multiple corruption-reducing relics: at least 3, IIRC. It also happens at a point in the game where your full arcane caster has reached level 9+ and has plentiful spellslots for AoE disabling spells: Grease, Glitterdust or Winter's Grasp (via Loremaster), Stinking Cloud with Corruptor, Heightened any of the previously mentioned spells, Phantasmal Web or Greater Command (via Loremaster) or Heightened any of the previously mentioned spells. If you expend 1 AoE disabling spell per encounter cast by a properly leveled and supported (Court Poet + Cleric) DC caster, you will have no issue with resting and corruption.
Until the big Stealth bonus items start showing up in Act 4 autopassing Stealth checks on the World Map is non-trivial without Aru.
Absolutely wrong. Stealth checks are trivial with a DEX-based Court Poet, especially Kitsune.
I don't. Buffers have more than enough spell slots, because only a couple of buffs are cast by an offensive full arcane caster: Reduce Person early on and Heroic Invocation in the later parts of the game. Everything else is cast by the Shaman, Cleric and Court Poet which do not cast offensively and can thus contribute all of their spellslots to buffing.
If you're restricting your party make-up
Proper party composition is always restricted. If your party does not have a full arcane DC caster supported by a Court Poet and Cleric or some other class that provides domains: it's trash. Whatever advantages you can think of will always be laughable relative to high DC AoE disables that dumpster entire encounters in 1 action.
you're trading off the opportunity to play with martials + Skald
A proper party has open slots for at least 2 pure martials of any variety, tank or damage dealer. That's more than enough. The only Skald that matters is Court Poet, the base Skald is worthless, utterly irrelevant dogshit.
You can get pets in a proper party without sacrificing anything important, if you want. I don't need them, because their AC cannot compete with a proper AC-stacker without wasting a party slot on a Brownfur for pet polymorphs.
Just another example of endgame thinking dominating
No, it's another example of your ignorance and lack of understanding of the game mechanics and proper party compositions.
