That's how it is in 3.0e at least. I'm not sure about AD&D, but Paladins have a minimum WIS requirement of 13 anyway IIRC, so it doesn't really matter.

"He can cast priest spells once he reaches 9th level, but only from the combat, divination, healing, and protective spheres. He does not gain extra spells due to a high Wisdom score, and his casting level is his current level -8, to a maximum of caster level 9 at the 17th level. His casts very few spells per day, and his highest spells are 4th level spells."

suppose my mind is getting rusty about add

And then use skill books to increase to 25.

Those didn't exist in AD&D, I think you needed a Wish spell to increase (natural) stats above 18.

It gives you a magical defense adjustment and lore bonus if high enough and a penalty to both if low enough. At least I believe those apply to all classes.
I never liked dipping below 10 on either Wis or Int because of the other bonuses. Lore's no big deal, but the Magic defense adj is.

Edit: I also wonder if the % of Spell Failure penalty would be used from the Wisdom once he can cast spells.

Special addition to Baldur's Gate, then? (and kept as files, but not used, in Baldur's Gate 2)

WIS doesnt give magic defense adjustment or affect spell failure rate. It says it does in the manual but wasn't implemented in the game. It's basically only useful to Priest and Druids for bonus spell slots and lore.

I always went buy the manual as gospel. I guess I've been doing it wrong all these years. Okay not a spell caster both Int and Wis will be a 3 or the lowest possible from here on out.
The skill books from BG only increased your attribute one point. I don't think there are two many of the same attribute skill books laying around. In that case 19 or 20 would be the max, unless you used Shadowkeeper to change them.

INT will affect how long you stay trapped in a Maze spell and also gives some resistance to Mind Flayer psionic attacks since they drain intelligence, so its more useful than WIS for non casters.

Ironically, the WIS skill book is the one you can find multiple copies of (3 possible, if you include the one found in the TotSC expansion).

What kind of a saving throw does your character use for that? Is the INT added to a die roll for the saving throw, or is it just a bonus like the magic defense adjustment.

So there really are people who are re-rolling for eternity to get 18 in stats everywhere?

Why don't just just put the godmode cheat and cease the masquarade? ;-)

Intelligence of Target -- Time trapped in maze
under 3 -- 2d4 turns
3 to 5 -- 1d4 turns
6 to 8 -- 5d4 rounds
9 to 11 -- 4d4 rounds
12 to 14 -- 3d4 rounds
15 to 17 -- 2d4 rounds
18 and up -- 1d4 rounds

Mind flayer attacks simply reduce your intelligence directly and once it hits 0, you die. So the higher it is, the longer you can last. I'm not sure how much intelligence is drained per attack - I think its 4-5 but I'm not sure. They also get multiple attacks per round so they can potentially drain much more than 5 very quickly.

Mind flayer attacks temporarily drain INT, but if you get to zero, you're dead. So higher INT means you can last longer against them.

As for the Maze spell, the table is:

Intelligence of Target -- Time trapped in maze
under 3 -- 2d4 turns
3 to 5 -- 1d4 turns
6 to 8 -- 5d4 rounds
9 to 11 -- 4d4 rounds
12 to 14 -- 3d4 rounds
15 to 17 -- 2d4 rounds
18 and up -- 1d4 rounds

There's no "should" about it. The AD&D 2nd Edition rules state that only priests (i.e. cleric and druids [and other optional priest classes, but those don't exist in the core rules or Baldur's Gate]), not paladins and rangers, get bonus spells for wisdom. As for wisdom requirements for high level spells, in the P&P rules there are certain such requirements (though not as you describe - I think that's 3rd Edition), and similar (but differently numbered) intelligence requirements for wizards, but as far as I can tell these requirements weren't implemented in the Baldur's Gate games.

Those Manuals and Tomes do exist AD&D 2E; they are listed among the magical items in the Dungeon Master's Guide.