Advice on Credit.....?

Ok, im 22 years old and I have 4 accounts open as of now. one is a charge account with an electronic store with a limit of 10,000 that was opened around a year and a half ago. I bought around 6,500 of tvs on it and paid them off within a year. The account is still open but not used. I have an auto loan that i opened around 10 months ago for 12,100 and still owe 7,600. I have 2 credit cards. i opened a capital one account around 8 months ago with a limit of 500 and then raised to 750. i got a green amex around 2 months ago then was upgraded to a platinum($450 annual fee) within 2 months of having the account. my experian score is 736 and transunion is 710. My problem is i need more credit on the capital one card and have called to ask for a CLI and was denied. i currently have 7 inquries with experien in the last 2 years with only 2 being in the las 6 months. i have only 4 inquries with transunion. Should I apply for another card with a higher limit or should i wait a little longer for some of the inquries to dissapear from my credit report? I am confident that i can get a better card(non amex) with a more generous limit. I max out the capital one every month almost. I need more credit with either mastercard or visa because amex is not accepted everywhere. I have never had a late payment ever. Any suggestions?