I often wonder about whether to keep spending the $$ for Platinum but a) I use a number of the features; and b) my assistant finds some aspects very valuable and forbids me from replacing it.

Useful things: a) I rented a car and had the rear window bashed in while skiing in Alberta. I had declined all coverage. They handled it with no problem. I paid nothing.
b) My wife went to Ireland and rented a car. Amex Platinum was, if I remember correctly, the only card which the rental companies would allow you to decline coverage. The insurance cost would have exceeded the car rental cost.
c) I use the CO and NW airline clubs and will use Delta -- I used to use USAir as well -- and only pay for AA and UA or AC clubs.
d) SPG gold is good, though I'd love SPG Platinum. As micro said, I recently stayed at a Sheraton in Sydney and called to make sure I was Gold while I was waiting in LAX. They upgraded with no problem. (Nice hotel, too).
e) the 2 for 1 tickets, which were the original lure, are never cost-effective.
f) getting all the car rental cards is also useful, though these might be free if you just asked Hertz, Avis, National, etc.
g) I think the Medical Evacuation insurance is very good to have.
h) I don't use the concierge, the restaurants or the travel agents. This was never a lure.
i) The magazine is hilarious. There are obviously a lot of people who want the Platinum/Centurion cards for what it says about them (to other people and to themselves). I am rich enough to stupidly spend lots of money. According to Amex, platinum card readers love the conspicuous consumption cast of the magazine.

I'd have to ask my assistant why she likes it so much.