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.

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.

Also, are there income stipulations to get the AMEX Platinum card?

Thanks everyone!