Fwiw, this is less and a less a problem with static languages. In the Scala ecosystem, for example, on-the-fly compilation is available with Play, or any framework that uses SBT [1] (Lift, Scalatra, etc). Edit, save, and your edits (and only your edits) are automatically recompiled and reloaded.
> more boilerplate
Not sure about that. Lift at least (maybe Play too, not sure) is about the same lines of code as Rails, less if you include tests.
1. github.com/harrah/xsbt
https://github.com/harrah/xsbt/wiki/Triggered-Execution
http://cookbook.liftweb.net/Developing+using+a+text+editor.h...
https://github.com/liftstack/lift24-s29-blank.g8#readme (still a work in progress, not debugged, but you can test the sbt "~ compile" continuous compilation directive)
Dynamic languages: faster to write something, less code, no time wasted waiting for compilation, but harder to maintain and a bitch to refactor. Need more unit tests.
Static languages: more boilerplate, slower write time, but man it's nice to get compile-time vs. run-time errors...