Valuable feedback, thank you for this! How would you feel about a demo video where I show you how to set it up and go through the features at the same time?
I agree that it would be helpful to show a simple use case on the home page. Maybe I'm not the target customer (although I am a soloproneur), but your user flow of (1) user clicking a button, (2) plunk receiving an event, (3) plunk sends an email, isn't really a problem that I have, since sending an email after an action is taken is pretty easy to manage. Are you are focusing on categorizing users into groups and sending them progressive emails?
A very big part of what Plunk does is giving you the opportunity to link multiple events together and delay emails. You can extend it to users that have clicked button A and B but not button C and send those an email after 5 days. Significantly harder to implement and a lot of code that isn't really used elsewhere!