Plone has a lot of infrastructure that would really improve Zenoss. This includes exposing content types through the ZMI, the Generic Setup/Quick Installer, workflow, advanced dashboard, portlet, and viewlet engine, and much more. It would of course, with some effort, be possible to port this to Zenoss, but Plone4Zenoss gets us there right now!
There is a vibrant Plone community which dwarfs the Zenoss community in size and prodigiousness. Plone has been around for a decade, has strong ISV support, and a roadmap well into the future.
The Plone ecosystem is vast in the range and functionality of extensions you can immediately incorporate into your site. From wiki's and forums to Skype to newsletters and mailouts - fairly much everything asides from network monitoring and management.
Plone4Zenoss gives you all of these benefits and is available for download here
Plone4Zenoss is commercially supported by Last Bastion Network.