I think the main advantage of a type system (e.g. Java's) is that it avoids a lot of stupid mistakes; and therefore does help refactoring because most "stupid" changes will simply not compile (rename a function but forget it's used in 3 other places? boom)
Static analysis with Spec might be a great booster because it gets you the expressiveness of Spec to static code reasoning.
I've used static and dynamic languages. When using a dynamic language, I usually don't miss static language features, except when refactoring and/or maintaining a large code base. It's the reason why I'm interested by Flow and TypeScript (in the JS ecosystem), mypy (in the Python ecosystem) and even static languages like Go. It's also the reason why I'm a bit reluctant to invest in Clojure, despite being interested by the language.
I think the main advantage of a type system (e.g. Java's) is that it avoids a lot of stupid mistakes; and therefore does help refactoring because most "stupid" changes will simply not compile (rename a function but forget it's used in 3 other places? boom)
Static analysis with Spec might be a great booster because it gets you the expressiveness of Spec to static code reasoning.