[ruuk]

you can get an add-on list through JSON-RPC. not sure if you can also get the current addon version with it.
if you can you could save current list. then start comparing it every X amount of time and that way notice if there's an updated version installed.

even better would be that we kept a list of recent updated add-on (or store addon update date). Perhaps something for the future.

Thanks for the ideas.
I was hoping that addon updates were "notified" like video updates so I can handle them in the onNotification() method of the Monitor class which I already use. I just checked that out and it turns out this is not currently the case so something like what you suggested would probably be the way to go.