my $textInner =
  '(outer(inner(most "this (shouldn\'t match)" inner)))';
my $innerRe;
$innerRe = qr/                  # 
             \(                 # Start with '(',
             (                  # Start capture
             (?>[^()]+)         # Non-parenthesis
             | (?> "[^"]*")+    # !!! don't work...
             | (??{ $innerRe }) # Or a balanced () block
             )                  # One time only, aka the inner one
             \)                 # Ending with ')'
             /x;                # 
$textInner =~ /$innerRe/gs;
print "inner: $1\n";
__END__

inner: shouldn't match