There is an inspiration cap on how much inspiration you can earn, and that cap is based on your current level in the craft. If you're level 1 in JC, you'll earn the exact same inspiration from a CP160 white item, a CP160 gold item, a CP160 intricate item, and a Level 10 white item, because the inspiration from all of those decons--from Level 10 white to CP160 intricate--exceed the cap that you have at level 1, so you'll only earn the cap.
This is also not exclusive to jewelry crafting--the inspiration cap applies to the other three equipment crafts as well and work the same way.
This is why I don't use max-level intricate jewelry for decon unless that character has reached around level 40 or so in JC. (Actually, CP160 intricates provide so much inspiration that they will exceed the cap even at level 49, so there is never any point where you'll get the "full" inspiration from them... but around level 40 or so is where the amount of wasted inspiration is no longer ridiculous.)