I agree with the previous post. If you do a lot of first class or business class international flights, then the miles have tremendous value to you, since these are very expensive tickets when purchased outright.
However, right now I'm finding there's a ton of miles to gain through sign-up bonuses, so I'm not particularly looking to add to those balances through regular spend. I'm satisfied that I've got a decent supply of miles for the next couple of trips, I'm looking for currency that I can use immediately instead.
"Cash is King". You can use cash right away to purchase any item that you want whether it's travel related or not. Miles have a much more restrictive use, and you run the chance of miles being devalued or being unable to use the miles due to a lack of award availability. My personal preference is to only sign-up and use mileage related cards when there's a good size bonus.
Plus no annual fee for the Fidelity 2% Amex, so there's no risk in keeping it idle while you meet the minimum spend on another new credit card.