I think it is worth dabbling to see how things are done on the other side. Learning Haskell makes dealing with Rx / Linq a bit easier - not directly but by flexing that functional-thinking brain muscle.
Having said that I still think of C# as my go-to language and enjoy programming in it, I think it is a great general purpose language and I am glad I am doing my production code in that. It's a nice mix of type safety (so prefer that to Ruby) but with plenty of escape hatches and meta-programming options (prefer that to the strictness of Haskell).
As a C#/JS-er the most useful languages might be Powershell and Typescript, and the most eye opening might be Lisp and Haskell.