The AP bonus is only in the amount you can store not the amount you get, so if you use your APs regularly anyway it makes no difference.
My premium just ran out and well it's got some useful features.
the small missions display was the best, everything was in a nice compact list so was much easier to look through. But other than that there wasn't much point unless you want to explore the pardus cluster, and really you not going to need to do this until much higher lvl.
If you've got loads of free time then the extra char is nice, although the third universe is really under populated, but fun to play around in, and there are usually loads of missions available everywhere. I found it a bit boring though cos all my chars were at the same lvl so all doing the same things. I've given up on all my chars but Marquis now, he takes up most of my free gaming time
Also you get to add a signature to your messages which is nice... but as for game playing advantages there aren't any (except storing an extra 500 APs and access to the Pardus cluster and sector). I was always too weak for the Pardus sector itself, I had to avoid all the creatures when I went there, but I could be useful especially in war time when the pardus sector becomes a massive war zone
Once I'm toughened up in my chitin and if war breaks out I might sign up again just for the warfare fun.. but other than that there are just little features which eases game play alittle but really don't add anything to it. My advice is wait until your bored of exploring the Neutral territory and want to explore the pardus cluster, everything else that you get is just toppings.