While your income affects your success in attaining credit cards and loans, it's not accounted for in your Fico credit scores.
Your scores are very good by the way. Maintaining your perfect payment history and low utilization will see your scores increase over time.
Are you aware of the American Express CLI process? Raising your credit limit will lower your overall utilization, and will look good to future creditors.
How old is your AmEx relative to your other cards?
Starting Score: 573 (Exp 10/12)
Dubious is correct. Citi Identity Monitor offers FAKOs. You may purchase CS from myFICO - achieving 800 takes time. Eventually you'll get there with low util, higher AAOA and a good credit mix.
I have had my Amex since 08' they sent me a offer in the mail for 30,000 points and jumped on it at the time not knowing much about credit. I did know about the Amex CLI increase but I always felt like I was better off not bothering them since my income is low at the moment. I honestly don't even know why they offered me the hard back in 08' my income was even lower than 
I didn't realize I was paying Citi to give me essentialy "fake" scores, kind of a dissapointing waste of money. Guess I will find a new service with real score like this website. Anyone know if the TranUnions score I get everymonth due to my Walmart CC is a FAKO as well? I am glad to know my income isn't effecting my score though. When you said a variety of credit should I apply for some more cards? I currently have my CC's, 2 auto loans and a student loan. Thank you again for all the help ladies and gentlmen. A plethora of great information on this website.
The TU score from Walmart is a FICO. You don't need more cc's ; property mix of mortgage, installment and cc's. I wouldn't worry about the proper mix- it accounts for a very low portion of your score. Util and AAOA is the biggest factor of your score.
That's great news on the AmEx. If you get another AmEx, they will automatically backdate it, so that it will show on your credit report as open since 08.
Your fico score will take a small ding from the inquiry, but will recover quickly from that. Your Average Age of Accounts on the other hand will receive a boost.
With your scores, it'll be a breeze applying for another American Express product. I'd suggest a card with no annual fee such as the Blue Cash Everyday or Blue Sky. Or both, even. Your income isn't terrible, and you could always be a little bit "optimistic" about how much you think you'll earn this year.
If you apply and get one, apply for the other on the same day, and there will only be one hard pull on your Experian report. And suddenly instead of having one 5 year old Amex on your report, you'll have up to 3 (if an amex customer gets declined, it's only a soft pull. It only becomes a hard pull if you're accepted).
In a couple years when you are looking for that mortgage, there will be multiple 7 year old accounts, and that one insignificant hard pull from 2013 will have already fallen off.