Everything is "kind of just there" in Yume Nikki, that's the whole point of the game.
>Does uboa have any meaning or is it just another event that happens that the fans have decided to assign a lot meaning to even though it could have no meaning?
That's just human nature. If I show you two bags and I throw them into the water, you will naturally feel curious at why one sinks while the other floats. With time theories will appear, trying to explain the phenomena. It's the same with YN, if you see poniko turning into uboa when you turn the lights off, naturally you will think that whatever poniko did represent deliberatedly changed into something grimmer and with some deeper meaning. Does that mean that anything like that is there? No, yet that's the fun of the game. The moment you realize the magician never took the bunny out of his hat the spell is broken and there magic just fades away.
I feel like I'm in the minority in saying that Yume Nikki has no backstory or hidden plot whatsoever.
In my brief experience creating a Yume Nikki style game I understand that as you progress you tend to shoehorn in things that don't have to do with your original plan but you found would make a cool addition anyway.
So far as I see it, things like Madotsuki's suicide and Uboa are purely in the game shits and giggles. It's so easy to add extra events as you go so you think why not. A bit of a troll on Kikiyama's behalf.
I think anybody who has worked in any project can see this happening.
I also believe kikiyama did a lot of things just for shit and giggles, but I still consider it fun to try piecing things together, made my own theories and I have more or less an idea of what I believe is happening. I think it's one of the cores that brought this community so close in the past, to share what one thought.