Will you get a comp upgrade by flashing Gold at check-in? Highly unlikely.
Requests are based upon availability. Cancun ocean front in January is in high demand and the rates reflect it. In fact, the hotel has a non-refundable 30-day cancellation policy, so that's as 'lock down' as it gets.
Optimistically, rather than throw the dice at check-in, contact Gold Reservations and request they call the hotel on your behalf well in advance of arrival. You may have to do so repeatedly until the Gold agent connects with the right person who has the authority to fulfill the request.
You may even have to do it in steps. The first round of calls may get you into oceanview. A second round may get you oceanfront. Plans do change and cancellations happen opening the door for the one who is persistent.
Have you taken your vacation yet to the Casa Magna in Cancun? I'm interested in the beach. A dredging company was about 5 miles away in late November. Please reply. If you haven't been there try to talk to Cairo the concierge lady at the concierge desk. Tell her that you'd really like an upgrade and you spoke to a couple from Cincinnati and we suggested you see her. I'd think that if a nicer room is available, she'd try to make it happen for you. The more you go, the more they recognize you and try to make your stay very nice.