Someone (likely not 100% in the know) told me recently that due to the popularity of the Centurion lounges, there was no longer an option for non Platinum/Centurion members to pay to get in.

Again, no test of reality that I can bring, but it might make sense to ask around at AmEx for those considering that plan.

Please let it be known that I am saying this not to dispute anyone who has posted, but just to pass along something I heard from someone who has been there and allegedly learned that.