IMO Jupyter notebook is a big step up in complexity from just writing a python script. You can put block comments in python script just fine. "let me spin up a local web server to view my comments and run my code in serial in an object oriented fashion" no thanks from me.
how do you upgrade some existing "thing" from a google sheet to a colab notebook?
I know of the gspread package for python... but I can't see how that gives you anything but the raw data from the sheet. any graphs and interaction (!) and such you would have to redo in jupyter.
One thing I would add is, sometimes when you need some extra complexity that's too difficult to express or build in Google Sheets, one step above it is Google Colab (or any other Jupyter notebook).
Before building a full blown app, I always ask myself: 1. can this just be a spreadsheet? If not, 2. can this just be a Jupyter notebook?
And yes, the integration between Sheets and Colab is great.