This is something people used to do with Sims 2 neighborhoods- someone would use someone elses, get it all decorated and filled up in their own way, and share it.
Now that we have the world editor, if you want to do this, go ahead! What I mean is, for example, you might have taken the Paradise world I made and removed all teh lots, and placed 20 or 25 10x10 lots, making it a thriving little island instead of a secluded paradise. As long as you've done significant work yourself, feel free to share your save file and link here so people can download the world.
I would actually encourage people to do this, because it would be fun to see new takes on my stuff by others. :D