What does luck do really? Is it worth investing points into? What difference does it really make?

It has been discussed before, so a search might be useful.

It does what it says, improves your chance of any action having a positive outcome. You should be able to increase your luck once each time you level up and still max all attributes without any problem. You normally level about 72/3 times in the game and if by chance you still haven't maxed the skills there are ways around it.

I was wondering if luck has anything to with the contents you find in containers, like amount of gold and magical items and the value of these items.

it has an effect on randomly generated loot. for example, a high luck would increase the chance of a particular soulgem being a greater soulgem as opposed to common.

i'm not a modder, so i don't know the algorithms and lists used to determine the loot. i'm not sure if it affects how much gold you find, or the times of equipment that's found.

it obviously has no effect on items purposely placed.

i suppose every time you use a skill it effects the chances of success slightly (attacking, casting a spell, sneaking, disarming traps, picking lint out of your navel, etc)

I've noticed that when I use Spellmaking, the chance that is shown while creating it is lower than the chance shown in my spell list. I suspect that that is probably entirely due to luck.

Your higher chance to cast the spell than you see in the spell maker is more likely due to enchanted items, potions or active spells that fortifies the skill or attribute associated with the spell, e.g. if you're wearing Mentor's ring which adds 10 to intelligence and willpower.