This may not be all that robust, but it is better than square one...

#!/usr/bin/perl -w
use strict;
use Parse::RecDescent;

my $grammar = join( '', <DATA> );

my $parser = Parse::RecDescent->new( $grammar ) or
    die "Error: Bad grammar\n";

my $text =<< "SUB_STDIN";
A nicely [[spaced]] link.
A poorly[[spaced]]link.
Another poorly..[[spaced]]..link.
A harder problem [spaced] link.
Yet harder still..]]spaced[[..link.
The real problem is [[spaced]] followed by ]] or [[ link.
SUB_STDIN

my $results = $parser->startrule( $text ) or
    die "Error: Bad text\n";

__DATA__

startrule: 
    <skip:''> bit(s) 
bit: 
    eol 
    | word 
    | space 
    | token 
    | punct
eol: 
    /\n[ \t]*/ 
    {print "<newline>\n" }
space: 
    /[ \t]+/ 
    {print "< >" }
word: 
    /[\w\']+/ 
    {print "<word: $item[1]>" }
punct: 
    /[^\w\s\[\]]+/ 
    {print "<punct: $item[1]>" }
    | /(?<!\[)\[(?!\[)/
    {print "<punct: $item[1]>" }
    | /(?<!\])\](?!\])/
    {print "<punct: $item[1]>" }
    | /(?<!\[\[)\]\]/
    {print "<punct: $item[1]>" }
    | /(?<!\]\])\[\[/
    {print "<punct: $item[1]>" }
token: link
link: 
    /\[\[(.+?)\]\]/ 
    {print "<link: $item[1]>" }
[download]

Notice: new test cases for bracket as 'punct'.

--hsm

"Never try to teach a pig to sing...it wastes your time and it annoys the pig."