You will receive upgrade offers, but not during the first year. The Federal C.A.R.D. acts prohibits increasing the annual fee before the first renewal. Card issuers have interpreted this to mean that they also cannot "upgrade" customers to card with higher fees, and they want to be able to show that they billed you at the agreed price.

You can, of course, apply for a Platinum Card and then cancel the Premier Rewards Gold. This isn't an "upgrade", you won't keep the same account number and a credit inquiry will be required.