The main reason to install vCenter is that you've purchased it already 
By the time you've bought two servers, a SAN, and enough VMware licensing to run three servers (you have) you really should try to swing one more server. That'll let you use what you've paid for - and you'll get high availability and all those nice things.
If you really needed one server - one server with local storage would have been far cheaper and easier to manage. And then all you'd need is one ESXi license.