Having flown as Gold for 2 years before finally getting to Platinum then onwards to Exec. Platinum, I can tell you there is a massive difference in the odds to getting an upgrade as a Platinum level vs. Gold. The main factor I think in the criteria for upgrades is: 1) Status level and 2) Flown miles. This might explain why on the occasion I got an upgrade in Gold, I was usually top of the list since I had well over 170,000 flown miles as a Gold status member. Not very common I imagine.

If you fly enough, the platinum retention might be worth it. But IMO, the biggest benefit to Platinum (besides the 100% bonus miles which is VERY useful) is the lounge access on international flights. I fly internationally a lot so that's important to me. So if that's not the case for you, perhaps its no real big loss.