3. If a particular game gets "old". Don't delete it and start fresh. Put all your stuff in a chest, switch to creative and /tp yourself a few km away to start anew. Do this enough times and rediscovering your old builds becomes a voyage of archaeological discovery.
I was going to do the exact thing in my Monster world, however, I've been noticing that the more I explore of my world, the larger the world folder becomes... so the reason I didn't take this approach is because the world save folder will be enormous. Rather unfortunate. I copy my world folder at regular intervals so I always have a current backup should anything go wrong, but when it becomes so huge it becomes a real pain.
But yeah... my thought was to go into the nether, go in a random direction for a good distance, and plop down a portal and step thru it. Wherever I end up, that's my new home and I have to build there. Except I never did it, due to the folder size issue.