I'm somewhat convinced you can replicate that last feature (staging arbitrary / sub-line pieces of your changes) through ediff-staging (E s), but ediff is a complex tool in itself, and I don't know how to use it properly yet.

(Ediff is a 2-way / 3-way interactive diffing interface, built into Emacs, with plenty of features for surgical diffing of files, buffers, directories and whatnot.)