Take a look at your network bandwidth usage in the middle of a typical, real-world render project for you. If you're totally pegging the gauge most of the time, then it might help. If you've still got some wiggle room, or you're just pegging now and then, it probably won't.
If you are consistently pegging, then start with one slave node and incrementally add nodes to see where your network is maxing out. If you normally run eight nodes and you peg at seven, then boosting your network isn't going to do much for you. If you normally run 24 nodes and are pegging at seven, upgrading your network could make a big difference, indeed.
Technical Director - C4D, Maya, AE, - Washington DC