Replatforming your website to a new web content management system is an expensive proposition. In fact, a CMS migration can be so expensive and risky, that I advised many of my CMS selection clients against doing it. That is not to say that there are not perfectly legitimate reasons to replace a CMS. The wrong CMS can hold you back and prevent you from seizing valuable opportunities. But one sure fire way to spot a foolish CMS replacement project is when it is justified by a return on investment (ROI) calculation that relies on future labor cost savings to offset the price of an expensive CMS.
The truth is, if you make a big CMS investment, you will probably spend more time managing your content and optimizing the experience for your visitors. Why? Because advanced (expensive) web content management systems allow you to do more sophisticated things like personalization, multivariate testing, and advanced analytics. If your CMS has these features, you better actively manage them because neglecting advanced engagement functionality is worse than not having it in the first place. Buying an expensive CMS to avoid the human effort of managing a website is about as silly as buying an expensive car because you want to spend less time driving.
If you must show an ROI projection to justify the cost of a new web content management system, focus on the top line. Talk about the value (or potential value) of your content. Talk about the opportunity to reach new markets or connect with potential customers in new ways. And make sure to set aside plenty of budget for people to operate and get the most out of that CMS. To learn about all that goes into effective an marketing operations program, see me present at the Now What Conference next month.
If you want to treat your website like a project where you "do the website" and then forget it about it for a few years, I would seriously consider ripping out your CMS entirely and build a nice static brochure website that you can cheaply host. If you just need to make occasional updates, there are lots of cheap and free web content management products available. Many of these products can take you pretty far as you increase the intensity of your digital marketing program. But if you want to go high end, your initiative will fail unless you build a competent marketing operations program that gets the most out of the technology.