Twisting bass strings is an absolute necessity when replacing them.  It
isn't something one does to "add another foot of length" exactly, but
what one does to prevent the strings from rattling and buzzing,
eventually.  It also allows the string to develop all its partials.

I don't like to get into the empirical discussion about what sounds
better, steel-wound first layer strings, or all copper strings.  Granted,
mass is mass, and it takes less diameter steel than an equal weight of
copper to get the job done.  But there are so many more factors in piano
tone that are so much more important than that one, that frankly, I doubt
if I could tell the difference between the two kinds in an honestly
performed test.

The power of a string in the development of tone is less its length and
more its bridge design and soundboard.  For example, there is, somewhere,
a concert Chickering grand built in about 1850 or 1860 (the kind the
Gottschalk played on, for example) that was recently recorded and was
said to have pegged the studio's recording meters at over 126 db! That is
louder than a full orchestra.  There were no steel-wound bass strings in
that piano, to be sure, because you can't buy them anymore.  (The artist
who played it said that his ears were still ringing from that session 4
days later.  I have the recording.)

As far as the crown of a soundboard having something to do with the
longevity of the strings, well of course, it doesn't.  Crown is used to
counteract the downward pressure of the strings against the bridges.  It
has nothing to do with sound production, except as insurance that there
will always be enough bearing against the bridges to provide adequate
contact by strings to develop their full tone, despite changes in
humidity and wood shrinkage over the years.  The crown of the board is
always across the grain anyway, and along the ribs underneath.  Some
piano companies utilize the curve in the plane of the ribs alone, and
others curve both to counteract the string pressure.

Too much crown is also counterproductive to tone, as is too much
down-bearing.  "Just a little" is about all you can say, since that
element, too, is a very minor one.  However, too much (percentage of)
down-bearing in any section of the piano causes any piano to go out of
tune faster, because it becomes more and more dependent on the vector
percentage of the vertical component of tension in each string in that
section.  By jogging the string sideways between two pins on the top of a
bridge, you create a "down-bearing" of sorts anyway, but at the expense of
sideways bearing points in the string that cause it to vibrate against
those touch points, around in two planes because of the "crank" they give
the string.  So the percentage of the vibration that is sideways is not
efficiently transmitted to the board and is therefore lost.

You can see then, the way a common bridge is pinned is  effective in
providing an artificial down-bearing, but at the same time, causes a loss
of power.  Everything is a tradeoff.  (Oh, by the way, I don't know how
that old 1850 Chickering was strung in regard to the bridges.  I've never
seen one).

Craig Brougher