I have Nagato, and I would recommend you to go for refines or something else, still refines or charms would be the best considering what events we have right now.

I tell you my honest opinion, Nagato is not a bad ninja, but its extremely hard to properly utilize him right now. When we get Edo 2 and Edo 3, with a wider selection of edo ninjas it will change, but atm its a waste to get him, and his price will surely go down. You may as well wait until you get ninjas to use with him.