There are one thing in this thread that I think have been overlooked:

You should have 2 or 3 TOTALLY INDEPENDENT navigational aids. And when on a
passage - I'm thinking about more than a couple of days out of
sight of land - you would want systems that are not visually, terrestical,
based.

A backup handheld GPS is not "independent" of your normal GPS. Of course it
can be used if your normal GPS has a failure and if driven by AA batteries
it can function if your lead-accumulators have a malfunction, but if the GPS
system breaks down or is closed down, it won't function.

So what are the options ?
Radio-direction-finders.
Loran. (Is it still operational ?)
But if you run out of workable batteries and your electrical system is down,
these will also be out of order. (Water can do many things.)

It would be better to have a system that works without electricity at all.
Consequent dead-reconning, a good compass and a mechanical log could be an
option.
Celestial navigation an other - and with the advantage that it is
independent of what you have previously done or forgot to do.

So for a long distance cruiser I think that knowing how to use celestial
navigation is still a practical ability.

I agree that most sailors will not need this knowledge.

3 things speaks for celestial navigation:

1. It provides a totally independent means of determining a position when
out of sight of land. It is independent of man-made systems and
electricity.
2. It is fairly cheap and simple. A good plastic sextant will do the job.
(Chinese brass is recommended, because it is nicer to work with.)
3. It is fun and interesting, and it adds to your basic comprehension of the
universe and your position in it.

You can probably live without it, but if you sail the high seas it will
increase your safety and probably your appreciation of the world you live
in.