Paul, if you are up for that, it would be tremendously helpful to have a video(series) that shows what aider can realistically do given a boring, medium sized CRUD code base. The logs in the examples are too narrow and also build not intuition about what to do when things go wrong.
https://github.com/paul-gauthier/aider#tips
In particular, this is one of the most important tips: Large changes are best performed as a sequence of thoughtful bite sized steps, where you plan out the approach and overall design. Walk GPT through changes like you might with a junior dev. Ask for a refactor to prepare, then ask for the actual change. Spend the time to ask for code quality/structure improvements.
Not sure if this was a factor in your attempts? But it's best not to ask for a big sweeping change all at once. It's hard to unambiguously and completely specify what you want, and it's also harder for GPT to succeed at bigger changes in one bite.
[0] https://github.com/paul-gauthier/aider
[1] https://aider.chat/docs/repomap.html