I'd like to do my CalDAV from the CLI just as I do my IMAP from
mutt, what is my best bet as far as clients are concerned?
More recently, a CalDav capable command line client called khal has appeared to fill this gap. I have been using it and integrating it with Mutt and it is working nicely. With some simple scripts, I can view calendar information in Mutt and then import it to
khal where it is then synched to my CalDav server and propagated to my other machines or devices.
It is still described as in "the early stages of development", but I have found it to be stable and simple to use.
The next step, according to the developer, is to use vdirsyncer as the backend for synching: it is set up much like OfflineIMAP, with Remote and Local data stores: synching between the two. Currently there is a vdir branch to test this functionality.
Calcurse does support CalDAV (still experimental) in the latest release. It's packaged for the most common GNU/Linux Distributions and BSDs.
There is a library in the project caldavserver that seems to be currently mantained (cadaver hasn't done a release since 2009) With the stock client you could do some of the stuff you need.