"Symbols" is a wonderful feature, but it needs some usability and feature improvements. Looking at Illustrator, from which the feature, as well as the name seem to have been derived, it is possible to "break" the link of an item to the Symbols library. Scribus should either provide this feature or another way to convert it to a normal item.

Users should also be able to delete Symbols from the library without having to open the Fills dialog (see: Scrapbook).

With the Symbols dialog open in Illustrator, it's also very easy to add a new item to the library: select item and click the "New Symbol" button. Done! (I don't think the choice of "New Symbol" is a good one, though; I'd prefer a more telling description of the operation).