Well I can't speak for whether it'll be widely used or not, I can just say that I'd use it myself, albeit sparingly, it'd be very nice if the functionality was there when I do.
The only other major use I can think of for it would be as an easy way to dupe a lot of items across plays. I also wouldn't be surprised if there's a lot of people interested in wildly overpowered "New Game+", exporting their late-game character and importing it at the start of a new game or something. Some people are suckers for that.
As for Copy/Paste of Items, I do know of the Export/Import functionality, and I've used it quite a bit when tinkering around, but it's slow and clunky. What I was thinking of was a simple Right Click->Copy, Right Click->Paste, allowing you to duplicate items on the fly, or between sessions (such as opening up one save in one window, copying an item, tabbing over to another window with another save, paste item).
