That's one of the downsides of using Starwood Amex instead of AA MC or Diners MC as your primary when collecting AA. Since I use Diners MC as my primary, I usually have no problems (with having to use different cards at different restaurants), since only once in 5 years have I seen a restaurant (no longer in the system) that didn't accept MC as qualified for iDine/RN.

However, I'm currently, temporarily using my AA Amex from Citi (which I got for the 25k bonus only) for dines (as it's an easy way to get most of the $750 min spend over 4 months), but I'm finding it so annoying how some fraction of the restaurants I regularly go to don't accept Amex (either outright, or not as qualifying for RN). So I have to keep track of each one. Yecch! I'm dumping this Amex for dines as soon as I get close to $750 spend.

Do some math on how few credit card miles you earn per year from iDine/RN purchases (compared to the many iDine/RN miles). Would it perhaps be worth sacrificing a few of those to simplify your life to standardize on using an MC or Visa for all your AA dines, even if you earn slightly fewer miles for the dine because it won't a mile/1$ card? (You could, for example, get and use an AA Bronze MC card, where you'd get a mile/2$. You'd have to do an awful lot of dines purchases in a year for that to be a poorer value than paying an annual fee for an AA Gold MC to get just an extra mile/2$.)

For example, the $160 you lost 1600 miles on you presumably got 200 miles on (160 + 25% eventually) on the SPG Amex. If you had used an AA Bronze MC you would have gotten 1600 + 80 miles. How many more dines would you have to have "wasted" on AA Bronze instead of SPG Amex for it to be worth the hassle of thinking at each restaurant "will this Amex count" (and risking such a mistake again)?