It's odd to me to see all the comments about not being able to use Amex. I have an Amex Plat and an AeroPlat and my wife and I do the vast majority of our spending ($150K+ annually) on the Plat card. We have a CIBC Aerogold Visa for those places where Amex doesn't work, but in my experience it's 90/10 acceptance/rejection.
Still don't know what I will do about the SPG Amex. SPG points are much more valuable than MR or Aeroplan points, so $100/year for the SPG Amex is a far better deal than $400 for Amex Plat. On the other hand, I want the lounge access and other benefits of the Plat and AeroPlat. Oh, the dilemma!