Go ahead and send pull requests with improvements. For a howto see: https://help.github.com/articles/using-pull-requests/.
MolecularViewer and MolecularSystem are stable.
SPADE loads MolecularViewer objects and adds a tabbed space underneath where Applications are loaded. Most contributions are expected to be Applications, where a developer creates a Tkinter GUI to access their code. Developers upload to github and users download the Application, through SPADE, either at cost or free.