To be honest in most of these mentioned languages you can reach the same goal. There is nothing you can't do with a language which can't be done in the other from the end user perspective.

But I have the odd feeling that while it is good to stick to a language (for strategic reasons) it is bad for improving code, getting better at what you are doing from a developer perspective. If I hadn't learned Python and wrote something in Python I would never be the same developer as I'm now.

When you look at for example Ruby and Rails there are so much better things you can do in the testing area. Ever used RSpec and Cucumber? You should know what I talking about. This is awesome stuff and it will let you develop a quality web app in days which is also fully tested.

What I'm trying to say is that YOU HAVE TO stay hungry as a developer about what is next BUT you should carefully choose what to you use in business. Looking at the same stuff (PHP) and going only to PHP conferences and hanging around only with PHP developer won't help you to get a better developer in the overall perspective.

Last but not least I want you to read Paul Graham's essays about Python people and why you will get better Python developer than any other:

http://www.paulgraham.com/gh.html

http://www.paulgraham.com/pypar.html