Jacqui,
May I make a suggestion? You are very kindly trying to come up with ideas for dementia. Have you ever spent time in a care home for those with dementia? That might be worth organising. Then you will get an idea of what the issues are. Even doing the course run by Alzheimer's Association for carers would be worth your while.
With dementia, a lot of the issues need calm, understanding people. These people need bucket loads of empathy, understanding, resiliance and creativity. As has already been explained PWD (Persons with Dementia), whilst lost and confused, can have a small, mad pocket of sheer breathtaking independence to their own detriment. Hence other ideas of robots helping PWD lacks insight.
A modicum of understanding of the world those with dementia live in will help you with insight as to their needs.