I would always do a clean new install, leave the old server running, export and import your nodes and credentials.
If all goes well turn the old server off, leave it there for 2 weeks and then remove the server. If the new server is a virtual, it could help if you don't use the buildin SQL due to IO load issues, but depending on the size of your environment you could try to run it all on one virtual, the advantage would be that you can have a snapshot backup that captures all at once SIM and SQL.