> Personally, I value that aspect highly because it means if I choose to work with a language that I can understand, read, and possibly contribute to the compiler if needed.

You would have about the same if the compiler were written in a lingua franca. For whatever it's worth, I have in the past had to work inside the gfortran compiler, and I wouldn't have been able to do that if it were written in Fortran.

Self-hosting (which nowadays often isn't "full" self-hosting, it's implementing a frontend and possibly parts of a mid-end only and letting a framework like GCC or LLVM do the rest) is useful because it proves that it has reached a certain level of maturity, as you say. Another advantage is that this gives you a non-trivial piece of software written in the language which can be used for testing and benchmarking. If you introduce a compiler bug, there is a certain likelihood that you will notice it immediately. This might not be the case if you only had small toy programs to test with.