ROI on Server ?

That's typically how ROI is calculated anyway....:)

But seriously, you can somehow get some savings through lower maint costs and less power.

The promise of greater uptime is more a cost-avoidance calculation, but every bit as valid. If you have any real business cost associated with server downtime, then the extra cost of the new server, with the more redundant and reliable hardware can reduce business risk, which management is probably more interested in than ROI. So if your cost of downtime for ten hours is ten thousand dollars, but the new server cuts the risk of that event in half, then there is five grand you may be saving in the future.

https://www.techrepublic.com/article/an-roi-primer-learn-the-basics-and-the-key-shortcomings-of-this-metric/1048998