They were costed based on the spells utilized, rather than the functionality comparisons. Items which involve multiple spells in their design thus necessarily wind up hideously expensive. Pretty much the only thing that the pricing guidelines are good for are static bonuses really. Anything beyond that cannot be easily compared in the same way.
The more abstract factors would be:
Niche vs General use - Effects that are inherently niche should lean towards expendable item costing, or they'd never see use at all. Permanent niche(that is, truly narrow) effects shold be priced less.
Combat vs noncombat - Combat-usable effects need to cost more, especially limited use/expendable items. Having a combat ability be only usable 3/day seriously barely matters at all considering you're in generally speaking, 4 combats involving a peak of 3 rounds each.
The inverse needs to apply at the same time, for items which require combat relevant actions, a standard action is trivial for a general use item, but nontrivial in combat for the exact same reason.
A further consideration is items with multiple effects that incorporate the above two, the activated value drops when there are multiple activated options on the item, because no matter how many are there, it wouldn't matter as you would only ever be activating one, maybe two. They should count against general charges and use limits however.
Blanket immunities/save or fucked effects- Depends on your view of rocket tag. Personally I'd lean towards making them more difficult to obtain, but thats mostly just me and shouldn't be considered in general pricing without a more sweeping revamp of the whole business.
