Not worth the bother, since it won't make any meaningful difference. A third credit card will help greatly. Consider OpenSky secured card - easy to open, and will boost score.
Another option, though some here frown on it, is applying for a Fingerhut card. Despite their products often being over-priced (less so, if one can take advantage of their various promos), is a cinch to get, and reports to all three bureaus promptly.
Key to Fingerhut is buy a product - doesn't matter how much it costs, though I'd suggest at least $100, and pay at or above minimum due for a few months without paying off. Especially critical if only approved for their Freshstart program. After a few on time payments, Fingerhut will often increase credit limit. Afterwards, payment in full for any subsequent purchases works out fine (no longer necessary to carry a balance), and strongly suggested, since their interest rates are high.
To get a feel where your credit is without taking a hardpull (HP) hit (won't affect your credit score), and possibly a viable option for your third card, if pre-approved under their more favorable terms ($35 annual fee) is applying for a Milestone Master Card ... https://milestonegoldcard.com/get-your-gold-card
Barclaycard Rewards Mastercard, which is aimed towards those with Fair credit and better, is another option to consider, but you're likely just short of qualifying - bookmark the link and try in a few months. http://www.findmybarclaycard.com/barclaycard-credit-cards/compare
