Sunny addressed the creation of Primecoin very soon after its launch. Many PPC supporters such as myself were upset and confused as to why he created it. If you look through here and Bitcointalk.org, you will see his answers (I don't remember off-hand where they are, sorry, but search the few days after the launch of Primecoin).
In a nutshell, and I may be off and remembering it wrong, but his reasoning seemed to me to be...
1. He noticed an opportunity to help PPC become better long-term established and it involved creating Primecoin as a temporary bridge to help steer people its way. Mind you, this is a very long term bridge of many years (5-10 maybe).
2. It's a 'bridge' in the sense that proof of work, in his opinion, won't last for various reason. At some point the masses will transition to PPC when realizing this reality and the benefits of PPC. PPC is ahead of its time you could say. But, Primecoin will also serve its own other purposes in its own little epoch and show the world that cryptos can help science and be innovative in some new and important ways.
3. This opportunity he saw had to do with making a better version of LTC, right now, and transitioning marketshare from that to Primecoin. Supporters of Primecoin would then be introduced to PPC by nature of a shared community (this one) and mutual developers (not to mention leader).
4. Primecoin was also a way to potentially make some profit in a way that's positive/helpful and not shameful (i.e. cloned coins, pump and dumps).
5. Sunny had the resources to make it happen and enjoyed the developmental challenge (PPC was a slow, long-term play he realized).
I know many people are excited about Primecoin, but I ignore it as I believe PPC to be the better design. Why would you pay money for a Primecoin when you could get a better coin (PPC) cheaper? That's my reasoning at any rate.
So buy up PPC now, when it's cheap, and be a long term player. Don't worry about Primecoin. Primecoin will prove to be a brilliant strategic play that helped PPC replace Bitcoin (unless I'm totally wrong of course).
You will then realize Sunny knew what he was doing and is a mad genius.