Well I would still be using the Explorer to assist in maximising points earn. If you have one Amex, then you are already not on the 18 month countdown for a new sign on bonus. If one did not have the Edge then yes you would probably just use the Dragon and try and milk the sign on after 18 months., and just hope it is at an attractive level.
On maximising points earn:
Edge: supermarkets including GC purchase for fuel etc (5% off and 3 points for $)
Explorer: For most other spend at 2 points per$ (Edge is only 1 point per $).
I also gained 6000 bonus QFF points last month on my two Westpac Amexes for getting two more supp cards.
Now if you had the Platinum you would not need the Explorer, as it generally earns at 2.25. But I am not sure it is worth it at present for me.
And there is the money it makes me each year. One perk of the two Amex is the Supps which allow extra $ to be earnt on the cashbacks. With my 2 Westpac Amexes that was $1500 back last month on the Marriott deal and $400 on Sony. This adds up over the year. With the cashbacks then if the Amexe's were only a points play then the points advantage is a lot less.
I will ditch the Westpacs though when there yearly fee becomes due as currently both are free. with less cashback earning ability I will have to then re-assess things.