Agree on all points, especially the laptop/car comparison. Both devices show very little overlap in application (even personal flight - new gods always seem to be zipping around on those hover-disks). The ring may be the more flexible of the two devices, especially if the owner isn't aware of it's limitations, but does have the will/imagination to pull it off. You mention Ice healing with it, and I remember in JLA that Dream had referred it as a literal "wishing ring."
There's another aspect I hadn't thought of, to the "can a ring make a box" question, which is: could a mother box make a ring? I'm actually leaning towards "no" although I have no evidence to back this up.