I only recently started playing Yume Nikki and I have a theory that I haven't seen anyone mention..My theory is that Madotsuki has Amnesia and In a way she is affraid of her past that she has forgotten thus she doesn't want to go out of the house,because he memories might not be that pleasant and perhaps her dreams are a distorted and twisted version of her memories like Uboa could be someone that bullied her or etc[that is just an example] Poniko perhaps her friend that did something horrible like betrayed her or something..and in the end when she gathers all the effects perhaps she got all her memories back and thus did suicide because of something she did not want to face
Seriously..!I mean I have herd a lot of theories but the one you made seems to make sense in a lot of points.After all dreams are almost never with a straight forward meaning.They are always twisted and distorted so this theory actually does make sense......To me at least XD