I LOVE the infectious dementia idea, and I think you could use it to incredible effect. I have a lot of contact with people suffering from dementia, and I know that, remaining within the bounds of the story, you could include incredibly sad, poignant moments, outbursts of hilarity, true life lessons, the list goes on. It's an amazing idea, with so many directions to explore, and I, for one, would buy multiple copies of it (one for me, and several to distribute amongst friends and family). I would say, however, that it is such a good idea, that you would have to be careful should you choose to churn it out in NaNoWriMo. If you take all the time needed to perfect it, it, IMHO, stands a very good chance of becoming a bestselling novel for years to come.