Probably not.
Your April 2014 EX at 626 indicates you had at least one late payment in your past? If so, then your scores are climbing as you continue to pay on time all your accounts. The best thing that is going to help your score is aging off any baddies (or significant volumes of INQ), and each new month you add with on time payment. You have the utilization down as low as it can go, and so simple passage of time is your best friend now.
There would be a short term minor hit to your score by adding another card, I had two apps last month, each one was 7 points on EX. That would come back over time, and so having another card eventually would not hurt, and may help a little, but likely not too noticeable.
On the other hand, if there is a type of spend that you don't get significant rewards for, that may be a consideration that you want to look into. Having cards that get you financial payback, whether it is a few percent on groceries or points toward travel, has some real world appeal long term. FICO scores are nice, but you are nearly to the point where you can stop worrying about them.
Your scores are good enough to get a good cc. I can't see why a couple more won't hurt. 
They do start to nic pick you as your fico score goes higher. They will always find something they think can raise your score. I did everything they said & now they're telling me a student loan would be a good idea! Not happening! I would use your own judgement. If you really don't need it, don't get it. I always think that before I get an auto loan, etc. CC's are great as long as you can use the rewards and use the card enough to get those rewards.
@Anonymous wrote:Your scores are good enough to get a good cc. I can't see why a couple more won't hurt.
Thanks Sandibeach. I'm going to hold off for a bit.
Credit cards are pretty easy to obtain right now. Economic shifts may not make that the case at some point in the future.
More generally, I'm a proponent if you're not doing anything else with your credit report in the short-term future (out to the year mark let's say) and there's a card you want (hopefully for a legit reason) which you have a reasonable shot of being approved for, take the swing. Get any negatives (inquiry, AAOA hit) out of the way and aging as soon as possible as a bunch of stuff is time dependent in the algorithm.
I do agree with Jamie's theory on file thickness creating a buffer... I have a couple of "tradeline farm" cards that I really don't do anything with other than some goofy recurring bills or small purchase items occasionally. Rewards non-existent but they have $0 AF so they're not really hurting me: I still have one of my original secured cards as it meets this criteria and the amount of the deposit isn't a big deal currently to me.
Anyway up to you, I wouldn't suggest a bunch of frivolous apps, but if there's 2-3 cards which fit your spending profile and no mortgage or maybe auto on the horizon, I'd seriously consider doing a small spree if there's time from your last applications... it's basically how I built my own portfolio over 3 years to 10 cards (though I closed one, $59 AF no thanks) and I am already seeing the benefits of AAOA buffering even with the comparitive youth of my own credit report. Also a potential buffer on number of revolving tradelines reporting a balance too if you worry about such things.
It won't help your score short term, but it will mid and long-term in my opinion; however, you can absolutely take your current set all the way to 800+ if you wish, just changes in your future report may have a higher impact than necessary.
