>> it would be possible to type just 'C-h v RET c' to customize it.
>
> You forget the need to switch to the *Help* buffer before typing 'c',
> don't you?

I have no such problems because of using windmove-display-*
commands where the prefix arg defines whether to select
the displayed window or not.

Maybe describe-* commands could accept the same prefix arg
where C-u will reverse the value of help-window-select
the same way as C-u of windmove-display-* reverses the value
of windmove-display-no-select.

> And that need to go to *Help* is, for me, the single significant
> annoyance with Help commands.  For example, I frequently want to look
> at the source of a function whose doc string I just requested, and its
> a nuisance to have to click on the button there or go to the *Help*
> buffer, find the button, and press RET.
>
> So how about some special prefix key and a keymap to allow invoking
> these commands from a buffer other than *Help*?

To look at the source of a function, a quicker key is `M-.'
or `C-u M-.' that reads a symbol name.

>> diff --git a/lisp/help-mode.el b/lisp/help-mode.el
>> index 48cf435f97..24b7ffaa2a 100644
>> --- a/lisp/help-mode.el
>> +++ b/lisp/help-mode.el
>
> No changes in documentation to go with this?

Here is the documentation: