Depends who's writing the new code. My new code generally doesn't need people to maintain it and those that do end up having to modify it are happier that I replaced the garbage that was there before me.

You can write new code with the intent of making it maintainable.

If your new code is clever shit nobody understands you probably shouldn't be writing code.

YMMV.

I use very, very cool language tricks in my unit tests.

Not in the production code.