Bootstrap menu – make menu entries with submenu not clickable

I am admittedly out on a limb here because to test this I’d have to install your code and create some menus to test it with, but…

Look in the Bootstrap_Walker_Nav_Menu code. Find this:

$item_output .= '<a'. $attributes .'>';
$item_output .= $args->link_before . apply_filters( 'the_title', $item->title, $item->ID ) . $args->link_after;
$item_output .= ($args->has_children) ? ' <b class="caret"></b></a>' : '</a>';
$item_output .= $args->after;

I believe that what you want is to wrap the code that creates the anchors in a conditional like:

if (!$args->has_children) {
    $item_output .= '<a'. $attributes .'>';
}
$item_output .= $args->link_before . apply_filters( 'the_title', $item->title, $item->ID ) . $args->link_after;
$item_output .= ($args->has_children) ? ' <b class="caret"></b>' : '';
if (!$args->has_children) {
    $item_output .= '</a>';
}
$item_output .= $args->after;