I'm not against replacing old systems, but this has to happen in incremental steps.

This way, if an implementation path doesn't worth the effort, just drop it and don't spend dozens of months with a full rewrite and realizing that you are spending a week to implement a CRUD for a simple entity. It's even worse when devs are new to the project and have no knowledge of the domain; I've been burned by this, never again.

At the end of the day, we are not in the research field, we are payed to fix business problems, to deliver something that brings a business value. Yeah, it's nice to write some really complex software that would make the system a lot more optimized, but we have to deliver it before our bosses are getting tired of excuses and pull the plug. Learned that the hard way.

Having been in this situation, as well, I find that the aging out of technology MUST be led by a CTO who is competent enough to know that tipping point of cost-benefit. Their job immediately becomes a political choice (pass the pain to the next guy) when the point has passed and it gets worse every new CTO. Some of these systems are HUGE (hudreds of millions of lines of ColdFusion, where I worked).

in a way it's quite a testament to it's utility.

Allaire were there with a workable solution, before jsp, php, (?) asp. Iirc only perl was serious competition.

I still sometimes see lotus notes '.nsf' links

The reason I have been left without product document is because Oracle bought the software the organisation was using. Cannot stress enough the value of keeping an offline copy of the documentation of a product rather than relying on a companies website or similar.

Edit: Also want to add software installation files are very important to keep offline as well.