Many thanks to all ( esp. mirod ) - this was *extremley* usefull info.
To refine my origional request, I wanted to see elements ( with their attributes ) and any corresponding values ( but with no recursion ) - if such values exist.
( This is because the element attributes themselves sometimes contain 'data' by their very name / existance )
My finished code, with an example of requirement / result :

foreach my $file ( @filelist ) {
                my $twig= new XML::Twig();

                $twig->parsefile($file);

                my $twig_root = $twig->root;

                foreach my $xpath_arg ( @xpath_args ) {

                                my @xpath_result = $twig_root->get_xpa
+th($xpath_arg);

                                foreach ( @xpath_result ) {

                                                print &complete_path($
+_);

                                                $_->contains_only_text
+ ? print ' : ' . $_->text . "\n" : print "\n";
                                }
                }
}


sub complete_path() {

        my( $elt )= @_;

        return '/' . join( '/', map { tag_desc($_) } reverse $elt->anc
+estors_or_self);

}

sub tag_desc {

        my( $elt )= @_;

        my %atts= %{$elt->atts};

        my $atts= %atts ?  '[' . join( " ", map { qq{$_="$atts{$_}"} }
+ sort keys %atts) . ']' : '';

        return $elt->tag . $atts;

}

Running : ./show_xpath_value.pl -x '//*[@keep="1"]'

/doc/elt[att1="1" keep="1"]
/doc/elt[att1="1" keep="1"]/elt2[att2="2" keep="1"] : foo
/doc/elt[att1="1"]/elt2[att2="2" keep="1"] : bar2
/doc/elt[att1="1" keep="1"]
/doc/elt[att1="1" keep="1"]/elt2[att2="2" keep="1"] : foo3
/doc/elt[att1="1" keep="1"]/elt2[att2="2" keep="1"] : bar3
[download]

Giving me just what I wanted ! Thanks again.