Yes and No! If the project is more than bunch of files, I won't change it, unless the client request me to do so, which don't happen very often.
But if the project is simple and doesn't cost too much due to downtime, I will play with it. Mostly I will start working on the code and use sub domain to test it. Once things started working fine, I will migrate it overnight!
Coming to your question, for the urge you mention, I will write a tiny service which can be used in existing projects. I used CI for a medium sized application but once I have seen Laravel, I couldn't stop wondering about it. So took some time, learn it and implement a tiny module of the same app using Laravel and I'm pretty happy about it. Now I'm planning to use Laravel for creating APIs for mobile applications. So instead of changing the project as a whole, we can create microservices, or some helper utility kind of things which can be pretty fun, easy and get us going!
After looking @mgiambanco reply, I would like to add that this applicable to side projects.
When it comes to employer, I'd be happy to do it, if only it justifies the cost and time of migration. To give you an idea, we've migrated a big transaction based project from struts to spring and it took us close to 5 months. Was it worth it? Hell yeah. Development times went considerably low, and associated costs went down. But if the project was already in Spring, then it makes no financial sense to move it to PHP or Nodejs(just for an example!)! So it all depends on factors!!