Dragonhunterq, I couldn't agree more. Crafting anything other than consumables is as much art as science. What I find most often though in my games (and this is anecdotal so not true of everyone) is that my players tend to craft items specific to numbers, bonuses.
They go through the hassle of getting Craft Magical Arms and Armor in the party somehow then obsess over squeezing out the most +'s for their money.
I feel like a lot of "special effects" or niche spells go unused but could make interesting and unique magic items. Take Call Animal for example.
The spell itself compels an Animal with a CR equal or less than your level to make it's way to you, sometimes from up to miles away. It can't be an animal under the handling of others. You have to select a specific type of creature you hope is close enough at the time of casting. Once the animal arrives it is Indifferent towards you but if maintained at that level or better it follows you around for the duration of the spell which is hours/level.
I have a guy in a campaign that is a Halfling warpriest (Divine Commander) 4/hunter 3. He has access to Call Animal and could cast this at CL3 to draw out, say, a Bristle Boar or something if he thought it lived nearby. But I've never used this spell in three levels of having access to it even though I want to command subordinates once in a while.
Instead, what if I bound the idea of this spell - calling a specific kind of animal to serve me, into an item? What would that look like?
I thought immediately of a hunting horn. The thing would send a clarion call to an animal I find prevalent in the region of the campaign. Hopefully one is nearby and answers the call. This opens up a whole list of other items I'd want, like something to make the animal trust me, items I can use to quickly buff the animal to a level where it'll survive in combat at this level and something to allow me to communicate with it.
Just from envisioning that one item I find myself daydreaming a whole array of gear working in concert to make my guy the "beastmaster" or something.
I find it more interesting using such less-used spells or special effects to design unique items than the standard +1 Flaming sword with a custom background.