The manual is very vague on this stat. Anyone know what it does and should my thief have a lot of it?

I believe, from having studied decompiled Wizardry 1/3 source that:
* Each character has saving throws for different categories; the base value of these saves are based off the character's race.
* Every certain number of levels (think it's either 3 or 5) improves your saving throws by one point; hence, at extremely high levels, this no longer matters.
* Luck further provides a bonus to saving throws.
* Saving throws apply mainly to certain attack types (for example, a Priest's saving throw determines wither they are petrified by Priest Blaster traps or just paralyzed), or whether status ailments from enemy physical attacks are applied (this includes level drain, I believe).
* Luck only protects the character with the stat, not the rest of the party. It does not affect the chance of triggering the trap, but might protect the thief (and only the thief) from it; furthermore, it might not protect against all of them. It does not provide any magical protection, not even against spells like Katino.

Anyway, I don't consider Luck to be that important, and if I were to have a lucky character, I would rather have it be a priest than a thief (being able to cure status ailments is more important than being able to disarm chest traps when your party isn't in good shape; treasure hunting can wait). For Thieves, in any case, Agility is far more important (and it's good for offensive casters as well, to nuke enemies before they have a chance to attack).

By the way, which version of Wizardry 5 are you playing?

Thank you dtgreene for that information.

I am playing the DOS version from the Wizardry Archives collection. I already played and finished 1 through 3. I did not like wiz 4 at all so I gave up on that one. It is really Wizardry 6 through 8 that I am interested in but I liked 1 through 3 more then I thought I would so I am playing Wiz 5 now.

Luck actually has another effect, at least in Wizardry 1:
* Should a party wipe occur (and the game sends you to the cemetery, your characters may lose some of their items; each item that isn't cursed will disappear if a random number from 0-20 is higher than the luck of the character carrying the item. (If a cursed item has been equipped, it won't ever disappear, so you can't rid yourself of a cursed item this way.)

Also, it looks like silence spells (but not other status spells) check a luck-based saving throw (which is, again, affected by level).