the_tags() doesn’t return the links but immediately echoes them. As that happens before the echo they appear before the span.
What you want is this:
echo '<span class="tags">';
the_tags('See also: ', ' · ');
echo '</span>';
or even simpler
the_tags( '<span class="tags"> See also: ',' · ', '</span>' );
As a general rule of thumb you can remember that function that start with the_ directly echo things, while functions starting with get_ return stuff.
So here you could also be using this:
echo '<span class="tags">' . get_the_tag_list('See also: ', ' · ') . '</span>';