It's worth noting that even if you choose the "upgrade" route, they'll still do a hard credit pull. You might as well apply for a brand new card and see if you can get a mileage bonus that way.

I realize you might want to cancel your Gold card, but keep the card numbers the same for auto-pay purposes, but have to adjust your auto-pay information with everyone else is a small price to pay for the mileage bonus you receive.

Personally, I plan to keep both the AMEX Plat and Gold PRG. Latter lets me accumulate miles. Former gives me a lot of travel benefits. I also carry the JPMorgan Select card which works at most places that don't take AMEX and lets me accumulate points toward domestic UA and Amtrak.