Yabut... Assuming the "Ordinary Person doesn't know much about boat
structure, so use a Qualified Surveyor before buying!" mentality, what
good would a personal inspection by me do? I will have a Professional
inspect the boat, and supposedly HE will find all the problems I would
have missed anyway.

Learn more now, save your headaches later. Go down when your hired surveyor
is actually going to do the job and learn from it.

Regardless, my Plan is to submit an offer contingent as usual on sea-
trial and survey. If accepted, THEN I fly down and do the sea trial
(which of course would include a "personal inspection"). If THAT is
OK, I arrange for a survey, and if THAT is OK, I buy the boat. Only
one flight down required, and that's after I've been assured that if I
like the boat, it's mine.

Again, flights are cheap... lots cheaper than surprises later.

Only problem I see in this is that 2 of the 3 boats I looked at last
weekend had BAD holding-tank odour throughout the boat - that's
something that isn't obvious in pictures!

That actually not always that hard to solve. Lots of time it's just a
matter of replacing the waste hoses. Use it as a negotiating point to get
the price dropped by a couple grand.