...
Artifact-level items should be granted by DM fiat, period. The rest need to be sprinklable in a campaign via more fiat, or some random placement so long as the DM can "tune" the ability. Like for example, the ring of feather fall that's wonky and on the fritz, about to burn out. Does the PC throw it away? Nah, but you wouldn't jump down too often, just in case it fails.
Here is where attunement can improve the situation. At 1st level you can wear the invisibility ring willy nilly, but when the Dark Lord is gathering his forces, putting it on draws his gaze to you, and his ringwraiths can see you clear as day even with it on. This is the type of negative attunement it should give. Super power but it's an evil item, and using it more and more will corrupt you. Or if the item is good, you still need to have a supreme will to control it, otherwise it will overwhelm you. So you can be invis'd for 10 rounds at a time if you just found it, or 1 hour at a time later, or even all day if you become Gollum-like in your slavish devotion to it. Just like the berserker's weapon that gives the fighter a need to kill his teammates if he can't quench its thirst for blood with more fodder.
I loved the description of the rings of wizardry. Those are definitely, to my mind, evil items, and wearing them over time would run the risk of the slain wizards' souls trying to take you over, or at least drive you insane and scitzo. Attunement can be a negative thing too. All magic should have a price.
Which is maybe why those plain vanilla +1 weapons are still sought out for : no negatives!!