When purchasing support, you should consider you are really buying an expert who really knows google cloud, but doesn't have special buttons to click to do things you couldn't do.

If a service you depend on is down, your support agent will be able to tell you it's down, but not speed up the fix.

Cloud support will have more information about performance black holes and limitations that the documents don't describe. They also will be able to advise on "is this design or that design likely better". They generally know how the backends of GCP services work, and their common failure modes, which is pretty hard knowledge to get from the outside.