Don't forget about support issues when you upgrade. If you decide just to upgrade a few systems, then you have a mixed environment which is much more difficult to troubleshoot and maintain for your IT folks, and much more confusing and frustrating for your users. One user will say, “Just go up to the Office Button and click Word Options.” The other will say, “What’s an Office Button?” This generates a call to support and costs, you got it, more money and time.
Conclusion
The most basic question is simply, do I NEED the new functionality, and is it worth potentially having to force everyone else to upgrade as well, considering all the hidden time, money, and support considerations?