Hi, guys!
I may be not the biggest professional in your case, but my feeling is that as simplier you do, the better results you get.
I recently had to migrate from datacenter to datacenter, including ZCS v6 -> ZCS v7 + 32-bit to 64-bit. And it was hard for me to get into this reinstalling issues. Somehow my ZCS v6 didn't upgrade to ZCS v7 at all, and no comments on my requests I got at that time. So I decided to make clean ZCS v7 install and move accounts via imapsync and with a help of exporting/importing of ZCS web client. But in my case it could be done manually.
I really do not know amount of data you have to migrate, which probably woud clear up atleast solution findings. If you can afford downtime, then just setup your new server exactly as the old one, and copy over all /opt/zimbra folder. Or better, if you use virutalization, just export or move VMs. There are very many questions to find out at first, to really give you any options or at least share some experience.
Backups and tests are the ones that really help, because ZCS forum has became very unresponsive during last couple of years. Probably because of too manu solutions or the fact, that guys who tried to do it some time ago - did it, and this issue is not their any more.
I can agree, that ZCS documentation, which comes with each ZCS installation, is purely stating the facts, which in most cases require aditional knowledge or experience, and in many cases is not explanatory. But that is OpenSource any way.
Here are some links, in case you didn't stepped over them, and if you give more specific requirements, I would look in my archives to provide you more:
Moving ZCS to New Server - Zimbra :: Wiki Guide to imapsync - Zimbra :: Wiki
Actually I like this guy very much. His notes helped me a lot:
Ajcody-Notes - Zimbra :: Wiki
And I actually liked this idea:
» Zimbra :: Blog
... but there was something wrong with my former mailbox system, so it actually didn't work for me.
Hope that helps, at least a little.