To stay on topic, I would say GO from SL is a great leap forward with the published benefits:
1) Guaranteed Y seats (72 hours), very helpful to get that V fare tickets.
2) One extra guest to the lounge, very helpful for couples, or bring a buddy
3) Better op-up chance (unpublished benefit)
4) Better service on-board (arguable)
I would say if you have a chance to get GO, go for it.