Can you scan the not so important stuff (ie stuff not needing originals) and put it on a disk to free up some space??
I'm not sure what I don't need originals for and what I do - but I will probably shred the stuff that's over 7 years old and just keep filing the more recent stuff.
Will probably sort it so each year goes in it's own plastic pocket or two to make it a bit easier for shredding in later years and finding appropriate docs later