The intention of those rules is that the player and the GM work together to figure out a balanced item cost. Some spells work with the given formula, but lots don't. Mostly the cost should go up from those given by the formula, and that's the GM's decision, not something the rules dictate and the player should be bringing to the table in terms of "what it should cost". I'd avoid adding any custom items like this until you and your GM are both pretty comfortable with the system.
At-will spells tend to be abusable, simply because the power of the item is only limited by the number of actions available.
Activating a magic item is normally a standard action. Making it an immediate action usually increases the cost of the item significantly.
The two spells you're talking about in particular are Hero's Defiance, a paladin-only spell that lets the paladin spend a use of lay on hands to heal himself as an immediate action, and Gallant Inspiration, a bard spell that lets you add +2d4 to any attack roll or skill check that fails within Close range as an immediate action.
I wouldn't have any objection to an item that let a paladin cast Hero's Defiance a few times per day, though at-will I'd probably balk at - paladins are pretty tough to kill now anyway, and giving a paladin a buffed lay on hands for every lay on hands they have seems a bit excessive to me. One or two times a day, though? Sure, not a huge problem at the high end of a minor magic item, say around 6k-8k. I'd probably have it occupy an amulet or helm slot.
Gallant Inspiration I'd be much more leery about. It's basically a +2d4 to all attack rolls and skill checks at the cost of an immediate action, because the degree of success doesn't matter much in Pathfinder - just whether or not you succeeded, and Gallant Inspiration gives a +2d4 to any check that didn't succeed. As a bard spell, it's reasonable enough - bards don't get a ton of spells, and giving allies a bonus is what a bard is all about. As an item that another character can use, I'd be pretty hesitant, and certainly not at-will. I'd compare it to items that grant hero points, as that's essentially what it's doing, though to a lesser extent. The immediate action requirement typically isn't huge, particularly for a non-caster, since non-casters usually don't have much to do with swift actions anyway. Heck, most core classes in general don't do much with swift actions - the classes in the APG, Ultimate Magic, and Ultimate Combat usually have more swift and immediate action things to do than anything in the CRB. Casters start to care about them at higher levels when they start using Quicken Spell, but until then only a few spells use swift or immediate actions.