Peter - Thanks so much for adding the built-in Send Pushover Notification action, as the author of the old plug-in I haven't had time to look at it let alone add anything to it in a long time.
And of course, taking the opportunity to add request for the new API parameter ttl. It lets you set an expiration date (in seconds) on messages after which the message is removed from the different applications. Since they added it, I use it for almost every message I send so i don't have to manually clean up the app as much.
Also less important (for me at least) is the timestamp API. I use this on some alerts where i want to be sure the alerts sort in the order occurred. This one is specified in a unix timestamp.