dgreeney: you can only buy a Tarjeta Dorada when you are in Spain. You purchase them at a Renfe office only.
I have been traveling all over Spain the last two moths. There isn't that much difference between Tourist Class & business class. Tourist class is fine. The seats are comfortable, the trains are clean. The main difference I note is that the business class section does not have many passengers! Thus it is quieter. The seats are 2 - 1 configuration, are a little more comfy and wider. Not a big difference, not enough for the $20 E price difference or more! Also, it does depend on which train you are on. The diferences vary. Some trains have plugs for your devices at the seat, some do not. Surprisingly the Ave trains have NO plugs except in the bathroom. If you need to recharge your phone or device while on the train, you have to sit in the bathroom and charge there!