Is the Go! action card ever worth playing?
In addition to cards, it is very important to consider tempo when deciding what moves to make in a variable-hand-size card game... if your hand is strong enough on its own merit without having to draw additional cards, that's great, but you're going to run into situations where playing the 'Go' as a money card and playing another card already in hand is not going to be as good as playing the 'Go' card as an action card and then playing one of the cards that were drawn by the 'Go' action.  

I would say that the only time that you should play the 'Go' card as money EVERY TIME is when it is the last card in your hand, and the last action you can take (but even then you're only betting that the 5 cards you'll draw at the beginning of your next turn are better than the four cards that you'd draw if you played the go card and drew two your next turn.)