Regexp::Common to the rescue!

use strict;
use Regexp::Common;

my @tests = (
  'foo(bar)',
  'foo bar',
  'foo(bar',
  'foo bar)',
  'foo((bar)',
  'foo(bar))',
  'foo((bar)))',

);

for(@tests) {
  printf "%12s", $_;
  
  s{ [()] }( )xg and tr/ //s
   unless m/ (?<! [(]) $RE{balanced}{-parens => '()'} (?! [)] ) /x;
  
  printf " - %s\n", $_;
}


__output__

    foo(bar) - foo(bar)
     foo bar - foo bar
     foo(bar - foo bar
    foo bar) - foo bar 
   foo((bar) - foo bar 
   foo(bar)) - foo bar 
 foo((bar))) - foo bar
[download]

See. perlre and Regex::Common for more info on the regex used.
HTH

_________
broquaint