I would completely agree with you if this weren't a C compiler project. In this case, the advantage of having a self-hosting compiler is huge! Among other things, you can use the compiler source itself to test the compiler, which is pretty cool.

I have worked on projects that were essentially "C with classes," and it was fine. I'm not saying every C++ project needs to go all out using every feature from C++ 11, but I didn't even see much beyond use of the string class here. It seems not worth giving up self-hosting to me.