Well, my personal quest is at an end, though not in a way that lets me give much help to others on this thread: I am now the proud owner of a fully-carved 1920s German flat-back bass - no maker's label, Eb neck, gamba shape, 42.5" scale. It's definitely 'well-loved' - it was formerly in the hands of an education authority, and has some scratched graffiti as well as accidental scratches. Lovely sound, though. It also has a fair few repairs, notably a quite long crack near the middle of the back (nowhere near the soundpost, thankfully) but they're mostly decades old; the newest (a crack in the back of the pegbox) is late 1990s and was repaired my the luthier who sold me the bass, who said it hadn't moved at all in that time so he was completely confident in it. He's been using it as his personal bass for the last 3 years while waiting for it to sell. It's got a new tailpiece and cord, new adjustable bridge, and helicore light-tension orchestral strings.
It cost me £1100, including a good second-hand cover (it looks like the Classic Cover from [Invalid or Expired Link Removed], mute and humidifier. It already had on it an Ashworth transducer (AJ301P, I think), which he sold me as second-hand for £50, less than half list price. (I've now taken it off to improve the acoustic sound, and it'll probably stay off for at least a few months until I'm ready to play in public....)
I never got round to going to Turner violins in the end - I had my great-uncle-in-law with me, who's played jazz bass for 40 years or so, and he was emphatic that it was better to get an old bass. Francois and David at Unison Strings seemed both honest and enthusiastic, and we were both very happy with the bass, so in the end we bought it without even going to see the new basses at Turner's.
Photos at Invalid Link Removed, though they don't do the finish justice and make the scratches look worse than they do in real life (and I appear to have my eyes shut, but hey, it's not a photo of me).