I agree that your internal network should be fine on IPv4 for some time using NAT, CIDR, or dual-stack technologies. But let me ask you this: do you ever have IP address conflicts? If you do, what is the cost of those IP address conflicts? The cost of a conflict is more than just the cost of your time troubleshooting the conflict. It is also the cost of the network downtime. Perhaps it is not that large for your situation, but it can easily run into the tens and hundreds of thousands of dollars for large enterprises.

As for utilities, there a number of free and paid tools that do a great job of not only managing IPv4 address space, but also help in the planning of and IPv6 migration when you get ready to make the move. Take a look at SolarWinds free IP Address Tracker, or if you need more power, look at IP Address Manager. The latter offers a free fully functional 30-day trial so you can try it our in your environment.