The pricing is probably off because the item doesn't precisely duplicate the effects of the spell. For instance, the Goggles of Foefinding use the Clairaudience/Clairvoyance spell in order to be created, but all it does is negate the AC bonus an enemy gets for cover less than total. Reading the spell description tells you it does a lot more than that!
That said, I did go through some items and can tell you that items that don't rely on skills are accurate. For example, the Crystal Mask of Detection grants a +10 competence bonus on Search checks. A check of the DMG guide shows that the cost of an item that grants such bonuses costs the bonus squared, times 100 GP. So (10 x 10) x 100 = 10,000GP...
...which is the exact price of the Crystal Mask. So, if the item sticks to the guidelines, then it probably works out correctly. It's when the item gets away from that that we run into problems. Though, I wonder...I'm gonna go look into something. I wonder if the reason the formulas are off is because of the Caster Level. BRB.
EDIT: Back. I think the issue with the MIC items that fall under the DMG formula that uses a spell effect as the setup is that I used the CL of the actual item, not of the minimum level used to cast the SPELL. To use the Belt of Battle as an example - Haste, the spell needed for it, is a 3rd level spell. Normally, to use it, you need to be a 6th level caster. The noted CL on the Belt's entry, however, is CL9. Not 6. Recomputing the results, the formula spits out a price of 11,000 GP (that's after the halving you told me to do, GM), which is a little under the normal price of 12,000, but seeing as how the item gives two different abilities (+2 bonus on Initiative checks in addition to the charges) and the flexibility to use the charges as you like, I can see paying that extra 1k easily.