Anyway, Nyx has now been rebuilt with MOAR STORAGE! Nyx now has a brace of three Toshiba P300 3TB drives to replace the collection of random older hard disks in it and my data folder has been largely restored from backups. Unfortunately there were a few casualties of the disk failure: my email database did not get cleanly backed up and Windows Live Mail refuses to touch it. Fortunately the emails themselves are fine (stored as individual files), just the metadata and folder structure was lost. That's been rebuilt from the online email servers and at some point I'll reconstruct the offline folders.
I also discovered that Windows Live Mail supports RSS feeds! And, by default, it subscribes to a MSN feed and archives all the posts. I apparently have nearly 100,000 archived news posts which weren't helping matters.
All that's left is to redownload all the not-backed-up stuff!