I think learning new things is always good, if anything I have worked along the years primarily with Symfony/PHP, but as a freelance you try to get projects regardless of tech stack, I've worked on projects using ASP.NET MVC, Phoenix, I've done iOS with ObjC/CocoaTouch back in the days, or Django, and I have the impression that being exposed to different kind of solutions is always enriching and you can bring back to your main stack some fresh ideas/approaches