An infrequently used application has to be as easy to use as possible. Unless you have very specific needs, innovation is undesirable. Every moment you spend making your app as obvious and familiar as possible to your users will spare them hours of frustration and avert the potential failure of the initiative your app supports.
In the early '00s I worked with a team which inherited an intranet content management system built by an external agency who paid no attention to usability while loading the tool with functionality for every conceivable situation.
The result was technically complicated, impossible to master and filled with unused features. The outcome was that nobody who trained to use the tool could ever remember how to update their content, so they asked the intranet team to do it for them, meaning the intranet team was overloaded with content work and could never do anything tactical, let alone strategic. Meanwhile, the intranet became more and more out of date as people avoided anything that might result in them having to change any of their pages.
A lot of money had been spent on the tool, so the organisation was loathe to replace it until it was pointed out how much it was costing them to have a team of skilled contractors effectively editing documents.
One of my colleagues adapted a site he'd developed for me into a simple content management system with five fields, of which the content manager only had to complete two of them: title and body text to publish a page. When we showed an office temp how to use it and she was able to master it within fifteen minutes, we realised how important this could potentially be and when a internal rebrand coincided with the gradual rollout of the tool, the take up accelerated.
The intranet was transformed within six months as word spread about this new tool for great-looking intranet sites which was so easy to use and within two years we doubled the monthly usage of the intranet.