For greenfield applications, chose whatever the customer ask for on their Request For Proposals, or suggest modern solutions if they leave it open to proposal reply.
On existing solutions, deployed for several years on the field, actually measure what it brings in regarding business value. Either in terms of reducing project costs thus improving profit, or improving customer UI/UX thus improving the value the customers get out of the product, specially if it helps them to improve their profits.
What I am against is just adopting tech that doesn't improve anything, sometimes even causes products to be abandoned or removed from the market, just for the benefit of a few devs improving their CVs.
I have taken part in a couple of projects where it actually happened. Architects were busy chasing the new shinny instead of delivering what customers actually cared about. In the end the product was canned.
How do you know what improves what if you don't use it in anger?
There are many ways to research new tech without touching the current product development.
Sometimes it is better to be the turtle than the rabbit.
Especially in the Javascript world, it's such a new field that new techniques are being invented regularly. I've seen old backbone applications that are essentially frozen in time feature wise, because the code is so cumbersome and coupled together (by the framework's design) that it becomes impossible to add new features without having to refactor/rewrite the entire thing.
I agree, if you have have a finished product that won't be getting many new features at all, then leave it alone. But if it is an ever evolving product with new use-cases and features being dreamed up regularly, that application should probably be re-written many times over.
As for CV driven programming, here is a real case from a long gone project.
Dumping a fully working and battle tested Perl scripts for application installation in several flavours of UNIX, for Groovy based ones built on top of Grails.
It really improved the business value of those customers having to deploy a JVM, executing scripts slower than before and what was a simple set of CLI commands turned into starting Grails and navigate via web pages uploading files.