Eschalon's ability and skill systems have a lot more depth to them than described here, but here's what we learned about them from practical experience on our zero-kill pacifist challenge runs through the game (mostly as mages, but also as rogue-like characters):
Eschalon Book II Abilities
Even if you win Eschalon Book II without ever attacking a single thing, strength is still useful since it enables you to carry a lot more treasure and provisions without becoming encumbered. It will also have a modest impact on hit points gained at level-ups (among other things).
We still didn't plug extra points into strength scores, since you can brew Ogre Strength Potions and/or cast the Ogre Strength tier 2 Divination spell, as well as find various special amulets, rings, or weapons (which you can carry but not use to attack) to increase strength scores.
This is important for lock pickers, and anyone who wants to use stealth, since it also supports the Move Silently skill. It also gives you some benefits to your armor rating.
Having a good dexterity score is probably a good idea even for a pacifist run as a mage in Book II: There are some locks that we weren't able to open even with a high level "Lock Melt" spell near the end of the game, so solid lock picking skills are recommended.
Picking locks also grants you a small amount of xp with each success (which increases the higher the level of the lock picked), whereas casting the Lock Melt spell doesn't give you any xp at all.
This gives you a better ability to withstand damage and improve resistance to toxins, elements, and diseases, and also gain more hit points at levelups, as well as natural hp recovery rates. However, we never invested many points in it in our builds, and didn't notice any problems.
This sounds like it would be important for stealthy rogue characters, but as far as we know it actually only impacts combat speed and armor ratings, so we never allocated any points to it. (Dexterity is the ability that improves your success rate picking locks and moving silently, among other things.)
This is a powerful attribute for all magick users: If you plug a large number of points into this as your most important mage attribute, it will cause you to regenerate mana points at a very high rate as you walk around (or pass turns performing other actions), and the mana regeneration will be even more rapid if you're able to rest.
There is also a skill called "Meditation" that also supports this, but because xp and level-ups are more scarce on pacifist challenge runs where you don't kill anything, we found it effective to focus only on a high Perception score (and never invest our comparatively scarce skill points in the Meditation skill).
Having strong Perception also increases your mana points gained at levelups, so it's probably a good idea to start out with a high perception score from character generation, if you're planning to play as a mage in the long-run.
Perception also works to increase magick resistance and the discovery of hidden objects (which is a passive skill that will work better the higher your Perception score).
This is important for Elemental mages, because it directly impacts your ability to learn and cast Elemental spells: You'll need a minimum of 15 INT for tier 1 spells, 20 for tier 2, and 25 for tier 3. (See the separate Magick section for what specific spells are available in each tier.)
Intelligence also benefits all magic users by increasing the amount of mana points you get in level gains, impacts your elemental endurance, and increases your success rate with the Lore skill.
Wisdom is the attribute that Divination mages need to unlock their three tiers of spells. The same minimum scores are required to unlock each tier: 15 WIS for tier 1, 20 for tier 2, 25 for tier 3.
Wisdom also impacts mana point gains at level-ups, and probably also resistance for things like diseases or curses.
Higher Concentration scores will increase your ability to disarm traps, and also increase your ability to carry heavy objects. It also impacts combat skills in some ways, and perhaps also magical skills.
(This attribute was a bit mysterious to us and we never plugged too many extra points to it, but anything like rings or amulets that increase your Concentration ability can only work to your advantage, as far as we know.)