IMO for A3 *G: If your already flying that number of miles and *A carriers are available and it's not going to cost you much/if anything extra than go for it.

At the end of the day *G mainly gets your an extra baggage allowance and lounge access. Extra baggage can be purchased directly and depending on the frequency of use may/may not be worth pursuing *G for.

As for lounge access, I wouldn't go out of my way or pay tons of cash to access most of the lounges available in North America. Even in many parts of Asia the lounges aren't that impressive IMO.

An AMEX Plat or priority pass can also cover you in some cases for lounge access.