If there are network constraints I would first look at moving to 10GB for your VM traffic. This might be the right time to look at NSX if you are going to push for that. I am going to have to defer to others to speak more on NSX. This should in turn decrease your latency, and bring a lot of network management under the VMware umbrella. Your network guys probably won't like this...especially if they are Cisco guys...:)
If your goal is to "Decrease costs (cables, DC space, power, cooling, administration) in the future" then the obvious choice would be looking into a blade environment. This should reduce the number of network connections, space, cables, etc...