The biggest question is often whether you should go haring off every wild idea that comes along.
Sometimes, yes. It's not unknown for the finished product to have no trace of the original idea. (Mind you, that may mean the idea comes back, "Hi, remember me? Write my story!") If the subplot is more fascinating than the main plot, it perhaps should be the main.
However, wild ideas should get careful inspection. Will this idea play nicely with the others? Or be induced to? If not, it may turn the whole stories into an episodic mess. Unity of theme is vital. Even if it's a great idea, it may need its own story.
What fits is a careful balance. Some stories are like books titled Poems -- you don't want any prose in them. Others are like Sonnets, where a heck of lot of poems really would throw it off. Alas, with prose stories, there's seldom so elegant a rule.
And if you do hare off after the wild idea? Look back carefully. If necessary, pull out the sandblaster and eradicate every trace of the original idea that hang about, vestigal but still preventing unity of theme.