PROGRAMMING LANGUAGES ARE LIKE GIRLFRIENDS: THE NEW ONE IS BETTER BECAUSE *YOU* ARE BETTER
That is how Derek Silvers concluded his article over on O'Reilly about a bad experience trying to rewrite his existing PHP site in Rails. How true!
Another key message from Derek's column, though he doesn't say it directly: there can be tremendous value in refactoring, and refactoring does not require porting or changing platforms. All modern languages and platforms are capable of supporting large scale high quality systems. Sure, there are differences, and pros and cons, to each for various applications. But those differences are in the noise compared to the differences in capabilities of architects and developers themselves.
The lesson to me is: if you have a day to spend to make things better, do you invest it in learning a new language or platform, or in improving your own skills? I invest that time in myself. Advantages from switching platform or language can be had, but those wins are usually longer term, and can be undermined by abandoning some of your previously built skills and fluency.