There are a few ways to help out with the progress of the plugin which are listed below:
Developers: Help fix/improve things by checking out the plugin on Github.
Localizers: The Lite version of the plugin has been localized and any support with various languages can help the entire community. To learn more about localizing WordPress plugins check out the translation page.
Users: By purchasing a copy of the Professional version you help continue in the effort of maintaining and supporting the lite version, which is has been downloaded millions of times by users all over the world.