Yes, those are good guidelines.
For me, more than any rational calculation, it's a feeling that I am done with that item and will no longer miss it. I might purchase a similar thing in the store, but that's because the new item has an edge over my older one, like better fit, better color, more contemporary design, etc.
The only thing i ever regretted getting rid of was my faux fur vest. But that was at the beginning of the season. I have honestly not seen a single person wear them over here this winter (they were, however, quite popular about 6-7 years ago when they first came around), so now I know that I wouldn't have worn it even it I still possessed it.
