Ideas springing from other ideas Options

[Jens of Zanicuud]

When I first decided to finally make my first more-than-a-hour-playtime-RPG, I've written down a plot with plenty of details about characters, settings, endings, even some character hand drawing.
That project was Countdown to the End, a story set in Earth's last seven days, in which you would have controlled one of the people who believed in the existence of a sort of ark starship, which could be used to leave the Earth before the Sun exploded. In the end you should have discovered that that ark didn't exist at all and was a metaphor of a sort of spiritual salvation, or something like that.

I begun designing it and scripted the whole Blood&Pain engine from scrap, I was ready to start mapping, I created a title BGM theme and even the title screen itself... when suddenly, another idea struck my mind and imagination.
I completely abandoned Countdown to the End and started developing that new idea, which would have become Tryadine Effect.
Three characters from the previous project became the main helper in Day 4, while the others were removed.
Blood&Pain engine remained and some of the mapping ideas were recycled.

So, in fact, an idea rose from the previous one and took her place, coming from nowhere.

I wonder... is it right to follow a new path springed from the previous one?
If so... have you experienced something like that, before?
And then... was that new idea actually better than the previous one?

Generally, I found that the secondary idea is often better than the previous one and is something more mature, such as the original idea was refined and upgraded, but maybe is just my opinion.

I'm just curious about that, since it's not the first time something similar happens, I just hope this isn't an offtopic...

Jens