I am confused as to what a Magic Item's CL is really able to do.
There are spells whose duration is set on the Caster Level, as well as the parameters of the spell upon casting. These spells are generally stored into a Magic Item, whether through Spell Storing properties on Weapons or Armor, or otherwise.
But a question arises when you try to adjust a specific item's listed statistics; does doing so give anything other than a harder Dispel DC?
Let's take a classic example with Boots of Speed: These boots are set at CL 10 and give this same amount of rounds of Haste as a Free Action per day, divisible in 1 round increments as the bearer sees fit. Would increasing the Caster Level of this item also increase the amount of rounds of Haste granted per day?
Another example is an item such as the Eyes of Charming: going based off of the CL of the item, the duration of the Charm Person would last for 7 Hours. If we increased the CL to, say 12, would the Charm Person spell last for 12 Hours instead, or would it still remain as 7 Hours (and have a Dispel DC of 23)?
Some clarification would be appreciated!
The rules assume you would use the price in the book. The GM woudl have to adhoc the price for a higher level, and depending on the item it may not do anything different than just make it more difficult to dispel. If the item is a something like a ring of invisibility that duplicates a spell then the duration increases, but if the item has a set number of charges, or a set duration then it makes sense to increase the duration, but there is no set rule for it. That is mainly because item creation is based on guidelines more than rules.
The caster level of the item, is simply the highest caster level needed for one of the abilities.
Changing caster levels of the abilities, require increasing (and paying) the cost of these abilities.
However nothing suggest that you seperate abilities cannot have abilities at different caster levels (In fact you can, since nothing stops a spellcaster from adding abilities to an item at higher level caster made before them).
Boots of speed as an example.
The use-activation haste is based on caster level 10.
If you want a caster level 20 haste, you need to double the price.
You could however raise the cl of the item (and thus the dispel resistance) by adding another ability. Using light as a command word once per day, for example, could be caster level 20 for 5.400 gp.
To answer your questions:
1. Boots of Speed. The caster level matches the number of rounds which matches the description of the spell, so yes, it's reasonable to assume that increasing the caster level should allow the boots to provide more rounds of haste. Likewise, a custom crafter could make boots as low as CL 5 for only 5 rounds. This would be at your GM's discretion, of course.
2. Eyes of Charming: The item says it works like the spell. You infer it lasts 7 hours because a CL 7 Charm Person would last 7 hours even though the item doesn't say this. So do I. Logically, a higher CL means more hours, like the spell. This is less of a GM's discretion and more of simply reading the RAW - it works like the spell and the item doesn't list a duration, so we MUST use the spell description and the CL to figure out the effects.