I'm still on CD11, as I said before. But browsing at the Corel site for the CD12 features, it seems that Powerclip has been improved so that the contents can also be trimmed to the shape of the containing object. Maybe this would be helpful in cutting out excess materials?
Also, I'm not sure about Sallybode's comment on the symbols being limited to vector graphics with no transparency. From what I have in CD11, almost anything can be saved as a symbol. Even bitmaps. Or powerclipped shapes. Then it's just a matter of dragging it out and reusing it. The instances can be rotated, scaled or skewed independently. Using symbols seems to work faster on my old computer, too, compared to clones or duplicates.