Imbuing an item with Owl's Insight

Question

According to the Magic Item Creation Rules, one can add the benefits of a spell to an item continuously for a price of Spell Level x Caster Level x 2,000 gp. There are modifiers for the spell duration, but the spell I am interested in, Owl's Insight, has a duration of 1h which is the basis.

Now, Owl's Insight is perhaps one of a kind in that it grants an Ability bonus directly tied to the Caster Level: +1/2 CL Insight bonus to Wisdom.

This is pretty unusual, as it means that its pricing is very different from other bonuses to Abilities:

• Enhancement bonus: +N -> N x N x 1,000 gp
• Other bonus: +N -> N x N x 2,000 gp
• Owl's Insight bonus: +N -> N x 20,000 gp

The initial price is steep, as it is only more advantageous than using the "Other bonus" formula once past level 10, however it grows linearly instead of quadratically, and since there is little limit to Caster Level, one could potentially obtain a ridiculously huge bonus (after Epic).

There is also no limit given to this bonus since it based off the Caster Level which is virtually unlimited.

Now, if one uses the -30% from being restricted to a class or alignment, one could in theory get more than a +10 bonus pre-Epic (<= 200,000 gp ?):

• Max Enhancement bonus: +16, for 179,200 gp
• Max Other bonus: +11, for 169,400 gp
• Max Owl's Insight bonus: +14, for 196,000 gp

So, I would have two questions:

• Are the limits on the magnitude of bonuses (I often heard that Enh. bonus to Ability cannot exceed +6 pre-Epic) solely designed by comparison with published items or are there rule(s) pointing at absolute limits to distinguish pre/post-Epic gear?
• Will a magic item that costs around 200,000 gp that grants my character a constant +14 Insight bonus to Wisdom unbalance a level 20 campaign knowing that it governs its spell-casting ability?

Answer 1

No limits are set, but guidelines are provided

The first way to determine the price of a magic item is to compare the desired item with a similar item (DMG 282). That means, pre-epic no items provide more than a +6 constant bonus to one or more ability scores, and in epic no items provide more than a similar +12. (To be clear, those enhancement bonuses to ability scores are easiest to acquire; other named bonuses are supposed to be more expensive.) The game just doesn't provide guidelines for items that grant bonuses beyond those, math notwithstanding. It's up to the DM if such items are available. And because the game provides no guidelines, the DM should probably disallow them or make their prices extremely prohibitive.

The shenanigans that one can pull using 7–33: Estimating Magic Item Gold Piece Values (DMG 285) are legion, and it's up to the DM to reign in unbalanced new items that employ that table. That definitely includes using the table in the way the question proposes.

The magic item suggested is unbalanced

A magic item costing 200,000 gp that grants a +14 insight bonus to an ability score that governs a character's ability to cast spells is unbalanced. Even if such a magic item mandates a magic item slot or has a special requirements on its use (which are hardly special when the magic item is created or commissioned by a PC who meets such requirements), a +14 insight bonus to a caster's main ability score is ridiculous. The impact on the caster's spells is mind-blowing, and the only recourse the DM will have against a character possessing such an item is creatures that are magically immune; even then, a caster with such an item will have extra spell slots from the item sufficient to prepare spells that ignore a creature's spell resistance instead.

Only in the most high-powered of campaigns can I imagine such an item being a reasonable purchase.