A compromise I could possibly see for pre-buffing would be the inclusion of "prepared" spells/abilities. Basically, you'd always be allowed one ability that would basically be an instant-cast within the first 5 seconds of combat (or maybe a different number of seconds. Or maybe just for the entirety of combat? But then you could kinda cheese it later on when you double-cast something).
This way, though, you couldn't go around beefing yourself up all day outside of combat, and you'd still have to decide WHOM to target with what abilities once combat starts, but there would still be a tiny extra element of strategic planning, and an opportunity to exercise preparedness at the start of combat.
That's about the extent of party preparedness I could understand, as "everyone be spellshielded and armor-boosted and fire-resistant and super accurate and flaming-weaponed!" is kind of ridiculous every time you're jogging about. And I'm sorry, but "Oh, that guy uses fire... WHICH PRE-BUFF DO I CAST HERE?! SUCH PUZZLE!" is not much "intelligence" and depth added to the game.
Yet again, we see the effects of the transition from tabletop to CRPG. In a tabletop game, you might enter a dungeon and cast some kind of flame shield. Then, you could do crazy awesome specific things and get out of super interesting scenarios using that. In CRPGs (so far), it basically just amounts to a combat buff. So, yes, in tabletop, it could be pretty interesting to see the ways in which you'd use buffs to get through places, and how it would affect lots and lots of stuff ("Oh, I can wade through this lava now, because I have a strong enough Flame Shield spell on me!"). But, when it just becomes shifts in combat numbers, no one really cares much anymore to play the Matching game with combat numbers. "Oh, you've increased your attack? I'll increase our armor (block-your-attack) numbers! Your attacks do poison damage? IMMUNITY TO POISON! Let's see how many things we can each negate on one another, to chore-ishly return us back to neutral! 8D!" Ugh...
Same thing with resting. Everyone's like "Blagh! Why is resting gone?! It's super important!" But it never is in a CRPG. It's just a thing that you do because you have to when you're low on resources, and the only "depth" to it is "you might cue a random combat 'ambush' encounter if you do it in a dangerous area." Imagine if 17 different things could happen whilst you were resting. Imagine if, in PoE, a number of scripted interactions could occur if you rested in different areas. So instead of this thing that you do PURELY to "get back to the game" with full health and mana, it could actually be a part of the gameplay.
So yeah... maybe one day we'll see CRPGs become advanced enough to allow players almost the same amount of interactivity as tabletop campaigns. That would be pretty amazing. I know it's not easy to do and requires a goodly bit of resources, so I understand kind of why we haven't seen it yet. Pillars is at least headed that way via scripted interactions, so that's cool.