NCM is nice if you have the same auto attendants, etc all around. It automates patching (meaning you can roll patches out on a schedule after hours). It's also nice for centralizing backups.
You can't do "set admin" though, meaning make programming changes to sets, etc. You can make a "template" which is handy if you roll out more systems.
NCM is nice for a really large environment (50 sites or more). I would say with 12 sites, if your environment is fairly static (meaning not a lot of changes, etc), pass on NCM.
Just my opinion.