4. While every individual part may actually last longer or shorter than ALE, depreciation is typically based on the average. Any life beyond that is borrowed time, and expensive repair or replacement may well be required soon.
Hull - 30 years
Diesel Motor - 25 years
Electrical Wiring - 15 years
Electric Motor - 10 years (in salt water environment)
Electronics - 10 years
Sails - 20 years (cruiser), 10 years (avid sailor) 5 years (active PHRF club racer), 2 years (interclub trophy winner).
4. Those are some seriously conservative lifetime expectations. Sounds like they were cooked up by West Marine to sell parts. Seriously though, unless you abuse your equipment, they should all last considerably longer than that. Except the sails - they are definitely on a flat use to wear curve. 40 year old motors and hulls aren't uncommon, provided they are maintained properly.
Au contraire mon ami.
Remember we are talking ALE.
Not maximum life expectancy, not 96th percentile on the bell curve...
Northern freshwater may do better, saltwater near the equator worse.
You are absolutely correct that some diesel motors may last 40 years or even longer, but others are killed by 20, some as young as 4 (not coincidentally about the ALE of a raw water pump impeller).
Anyway, the actual ALE figures aren't so important, the point is, parts depreciate in value within this period, fast initially and then tapering off.
I hope you considered this realistically into your plans.