Today I read "If I could open an old document that already has right settings, and save a New Document Preset from this existing document, it would be a big timesaver."
That’s what scripts are for.
This ZIP-archive contains two script files.
The one ending with "_menu.jsx" can be installed in your Startup Scripts folder. Restart InDesign and you’ll have a new menu entry in your file-menu.
The other one can be installed as any other script in your Script Panel folder...