You are the only one that can really answer this question. Lounge access can be purchased (either one off or annually) or gotten via certain credit cards (which you note). How often do you check bags? How many do you check? What would an annual pass cost you? Run the numbers and see where you come out. Also note that you aren't getting into the lounge with A3 after achieving gold unless you are flying *A - so a Priority Pass or something might be your better bet depending once again, on whom you fly and all that.