If you need to touch a lot of places for refactoring on a regular basis, that should tell you you're not doing something optimally. If you write your tests so they are dependent on internal details of the other code, that's a warning sign too. Add to that, that at least in my experience, my Ruby code bases tends to end up far smaller than my old equivalent C code, and the problem tends to be a lot smaller than one might imagine.

Yes, you need testing discipline, but you need that with static languages too - if you think you're ok just because the compiler didn't complain.... Well, that's just a false sense of security.