Originally Posted by dovergator

I'm looking into getting additional credit cards purely for the sign up bonuses. Currently I've had an Alaska Airlines Visa card for nearly 10 years. I've also had a United Visa for nearly a year.

My concerns:
The potential for diminishing my credit score as a result of applying for new credit cards.
Yes, getting new cards often lowers your score. So you have to ask yourself is there a reason why you will need to maximize your FICO score in the next year (applying for mortgage, car loan)? Usually it is a good idea to stop applying for any new cards at least six months before you plan on applying for a loan.

I received a waiver on the annual fee for my United card for the first year, but in March I'll need to pay $75 to keep the card. I've paid $75/year to keep my Alaska Airlines card. I would like to not pay for the annual fees, but am concerned that if I cancel cards and apply for new ones, my credit score will take a hit.
Your credit score goes up and down depending on your actions. Once again, you ask yourself which is more important to you over the next six months, a big sign up bonus, or maximum FICO score.

Also, are there income stipulations to get the AMEX Platinum card?
There might be, I think the main requirement is that you can come up with the $450 for the annual fee. You probably can't be a student with less than 18k income, but you don't need 100k either.