How much does mileage verification really matter on older JDM cars?

[abdulsamad]

A UK-based buyer has been looking at a few older JDM imports recently and is wondering how much mileage verification really matters once a car is 15-20 years old.
Most people seem to focus on mileage when discussing the best used cars in UK,but with imported Japanese cars it feels a bit more complicated. Some examples being considered are an R34 Skyline, a Toyota Crown Athlete, and a Honda Stepwgn, all with varying levels of history and paperwork.
The budget is around £8,000-£12,000, and a couple of cars have auction records showing lower mileage, while others only have UK MOT history going back several years. DVLA records look fine and the MOT history seems consistent, but there is still some uncertainty about what happened before the cars arrived in the UK.
Is verified mileage something that buyers would walk away over on an older import, or is overall condition more important at this age?
A few specific questions:

• How much weight should be given to Japanese auction records?
  
• Would insurance companies care if mileage history isn't fully documented?
  
• Has anyone bought an older JDM car with incomplete mileage records and regretted it later?
  
• What signs of wear usually tell the real story regardless of the odometer reading?
  

Also interested to hear from mechanics or long-term owners. The best used cars in UK often get judged by mileage figures, but with older imports it feels like condition, servicing, and previous ownership might matter more.
Curious to hear what others think.