To help shed light on your idea...
1. I don't believe any 1 body of Pain is important to Nagato. This holds true except for Yahiko's body, and the survival of Konan.
2. Pain does not "need" any of the bodies because of their past abilities. It is helpful for Pain if the individual body is "powerful" , but it doesn't affect how he uses his own abilities through the "host". This is EVIDENT because Pain sent each body off on its on to find Naruto.
3. Pain depends on the View Point of multiple bodies in order to maximize his sucess rate of winning a battle. When fighting Jiraiya, he chose which bodies to bring out, and for a reason. Apparently to Pain, 3 bodies is sufficient to win a victory. ALSO, he uses multiple bodies in order to "cover his back." When fighting Konoha, Yahiko's body is the only one of Pain that is being "looked over" by another one of his bodies. This shows the importance of Yahiko's body to him.
4.
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Yahiko uses water element.
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Nagato uses wind element.
I hope this helps shed light on your question....