But the ability to simply manage and apply patches via a GUI does have an appeal and less chance for mistakes letting the manager take care of it all.
I agree, but for the host which on which vCenter Server is running, you cannot use Update Manager anyway, because you'll need to shutdown the all VMs, including vCenter Server.
Patching a host with the VMware image, or even an OEM image/offline-bundle can be done from the command line using a single command, so you shouldn't have to worry much about this.
Don't get me wrong, I'm not saying that Update Manager isn't useful, but in some cases it's easier without it.
André