This definitely falls into the bells and whistles category, but when you start to build complex nested workflows, it gets difficult to manage all the module parameters, since some may be buried deep inside the nested workflows. One possible solution that would be pretty cool would be a "configuration module" that could centralized key/often changed parameters to one location in the highest level of the workflows.
It could be something like double clicking on the module opens a gui that lets you add parameters, logically group them, and change their values. You could then assign some sort of identifier to the appropriate input of a module. When the module gets executed, it would be passed the associated parameter value that was set in the configuration module.