I do notice quite some people focus the autodiscovery part where for me that's less of an issue (I do agree it would be VERY nice). The OpenWISP configuration on each AP is limited to: set IP address of controller & shared secret and click OK. The rest is all magically done for you by the controller.
I do like the 304 idea, in practice it uses the same conceptual idea as the OpenWISP system: check if the MD5 (instead of SHA1) for the current config and the controller config are still identical and download and apply if not.
An important reason I why chose the OpenWISP is that they "just work", are well tested and included in the OpenWRT package list. My main goal is to keep the OpenSOHO project as small as possible ;)