As it turns out, the shut-off valve I replaced was fine - the filter on the tap had become so clogged with the sediment of a years worth of resting, that water couldn't push through it - a two minute fix. I did try to clean out a very slow waste line - disgusting job - hair, brown greasy gunk, some orange stuff (?), and who knows what else.
However, at the end of the day, albeit with a slow drain, we have one bathroom that while still decorated in horrifying brown floral wallpaper, is actually spotlessly clean. Tomorrow the floor sanding starts....
On duty: Maurice, Kirsty and me
Man hours of work: 15 hours
Cumulative hours: 51 hours
Cost of parts/labor: $347 (for paint, plumbing stuff)
Cumulative cost since purchase: $577