If you have a large working corpus of code in Blub, you absolutely shouldn't replace it just because a new version of Language on Locomotives comes out.
What you should do is exactly what patio11's doing here: evaluate if an upgrade brings you something that offsets the disruption the rewrite will cause.
For me, this also includes factoring in whether or not I'm going to be actively developing the application in the next year. If so, I do things like keep the framework versions current just so, nine months down the line, I'm using a framework version that I can still get docs and plugins for.
