I wouldn't worry too much about the goldfish preference for real or fake plants. It will learn sooner or later than fake plants aren't real tasty and then it will ignore them.
You pick whether or not you want fake or live plants based on your circumstances. Taking care of live plants require special lighting, fertilizer, Co2 injection in some cases, and other factors. Not everybody has a lot of free time to dedicate to taking care of the fish and the plants at the same time.
Just my 2 cents on this subject.