The actual upgrade window matters less than the fact that Platinums are prioritized above Golds in the upgrade order. Yes, it's nice to know you're getting upgraded 72 hours in advance, but it doesn't always happen. Even if it's down to the wire at the gate, a Platinum has a much better chance.

The other key benefit of Plat vs. Gold is that Plats get access to OneWorld Business Class lounges when flying coach internationally. Check AA.com for their definition of "international" in this case.