@Rosali
I have installed the version you sent me and i have two things/suggestions.
1. IMO you are one step from making a public calendar. Is it in yours TODO? Maybe something like in globaladdressbook, where is a global user? You could also make a public-calendar admin group to insert/delete events?
2. In Calendar Feed options, (IMO) it will be better to make a token-generate buttons (one for red-only and one to read/write).
If you have another version, you can send it to me for testing.