If you have a basic understanding of C/C++ and no real need to use it... No. It is a great language to know and understand but it doesn't do you any good unless you can apply it somewhere .
Dig into Python or Perl a little; these are excellent utility languages to know and can also be used for larger applications. For simple toss-away apps that your likely to need at some point, they are worth knowing. If you’re focusing on web development, ruby-on-rails might be a good to learn/gain experience with; or focusing your efforts on some of the PHP frameworks might pay off.
Also, don't bother learning Perl or Python, Perl isn't so widely used anymore, and Python has never really caught on to the mainstream. You're fine where you're at, and you will be much more prosperous developing for the .NET framework - just get on learning C#!
Perl's pretty mainstream. check out http://www.perlmonks.org, http://www.cpan.org, there's a TON of stuff going on there. Python and Ruby are excellent as well. I'd recommend learning C++ just because there's so many programming concepts behind it that are crucial to learn, it helps you design good software and layout your code much better if you learn it correctly. It's also excellent in GUIs and such. I, personally recommend learning all that you can.
2 things...learn as much as you can and learn as much as you can.
There are principles and uses for all languages.
However, it looks as though you are heads-down for web tech and languages, so csharp and scripting languages like perl, python and ruby should be your next choices. If you are doing more work on windows systems, I would script the three scripts and go to the .NET framework.