The impact on maintainability is about what you'd expect. Maybe, on an abstract level, the software isn't as complex as what you can do in Ruby, but the verbosity of the language brings its own maintenance challenges. I can't speak to Ruby specifically, but, in practice, I haven't found that I'm all that much more afraid to change things in a large Python codebase than a large Java one.

I'm now coming to think that the real challenge is dynamicism in general, regardless of whether it's built into the language or implemented as a library solution. So, if Java has an advantage here, it's simply that it tends to discourage people from overdoing it by making it awkward to do.