No simple answer to this one.

You will get the same bonus miles.

Platinum will give you an edge on upgrades; if you fly cheap domestic economy fares then Platinum is certainly better than Gold.

If you travel international/intercontinental economy, Platinum will get you Elite Plus which gives you lounge access, where Gold does not.

With Platinum you also get two free award ticket changes per year.

Finally, Platinums also get to pick between gifting someone Silver status, 4 (heavily restricted) systemwide upgrades, 20k bonus miles, or some gift card thingy.

If these benefits are worth $6-700, then go for it.