You can always call and ask if you are eligible for the Amex Gold Card. Typically, if you have a credit history with no adverse notations, they will be more than happy to offer the Gold or Platinum card. The pre-approvals are typically handed out to everyone, so I wouldn't put to much weight into them.

If you do have trouble with upgrading your card, maybe you can try to upgrade to the regular Green Card and then upgrade to the Gold card. The only experience I have is not with the Student card, but the upgrade process is typically quite easy.