OK, for whatever it is worth: tonight's flight is F4 A4, meaning they are still selling F seats. Also they are selling J and Y seats, so not much chance that people will be upgraded. The seat map shows only 6 out of 14 seats selected (plus 2 blocked, one of which is 2A, the UM seat). This would all suggest that there is a reasonable chance of getting a miles upgrade at the airport.
In your favour: EK will not give status members 'free' upgrades like US based airlines tend to do. If no-one is prepared to pay cash or miles to sit up front (or in front upstairs in this case), the cabin will have empty seats. I am not a regular F flyer, but in my limited experience I have only once seen a full F cabin (and that was when the flight was jam packed and I got an op-up..). Others here will have a better view on this.
Looking for upgrade availability a month ahead: 4 out of 7 days show at least one seat available for upgrade.
All in all, there may be a reasonable chance that you 'get lucky' at the airport. Whether or not that means that you should convert those AMEX points is entirely out of my sphere of competence / interest.


The mantra though is: if you want to fly F, the most certain way to do so is to buy an F ticket (or upgrade as you buy a J ticket if there is upgrade availability)