Hi everyone!

Long time lurker here, hoping for suggestions and guidance on upgrades

My wife and I are traveling from JFK to GRU (Sao Paulo) on Delta. We have the 'X' class fare on the way there, and 'L' class on the way back. I also recently opened the AMEX Delta Gold card, which gave me 50k miles. But when I bought the ticket, there was no 'pay with miles option' and the round trip fare would have been something to the tune of 80k per person. When I asked if I could upgrade using points, I was told I would need to upgrade to M or L class, which is an additional $800 pp. I currently do not have status with Delta, and EC is coming up as $139 per person per leg. Nearly all of first class and EC seats are available both ways.

What options do I have, both flying there and return? Is there a chance that I can get an upgrade to EC or possibly first on any leg? Are the same-day upgrades or standby options something that I can hope for? I have an AMEX platinum, which will give me $200 incidental reimbursement, which I am willing to use but am hoping to get the most bang for the buck.

Thanks for your help!