You probably won't listen to my advice but on the off chance you do I'll just say that I don't recommend you bother.

He is a really cool looking ninja there's no denying that, however he is really overpriced. There is a possibility that you could get two really useful ninja for the price of 4* Kyuubi (like Jonin Minato and Masked Man for example) I know its really alluring to go after a ninja that not many people have but hes not worth the price.

Just so you know that I know what I'm talking about I have an account with 4* Kyuubi on it and I have had it for months and months. I use him in the main team for that account (water main, roshi, kyuubi, sailor sakura) and while its a good team I would never ever pay the asking price for him. The original owner got really lucky and pulled him in lucky stars (back when they were giving 50 frag jackpots) for about $70 worth of ingots. I haven't even bothered doing the math on it but just looking at what they are charging I know there is no way its worth it.

Hopefully this helps, I just didnt want you to go all out and buy him and then be disappointed and wish you didn't.

Sorry it took me a while to get back to you. I'm not on the forum all too much anymore.

To answer your question I would absolutely 100% go for power items now. Especially when there is a good spending rebate like Fuku deals (launches tomorrow) because now that you have some B.A. ninja you want to have to power to make those ninja as useful as possible. Cave keys, charms, myoboku gifts, unbound runes, refines, etc is where I would put my money.

If you catch a 30-40% off advance refines in treasure of the sage before the new events I would buy all of them. One of the high powered players in my group said it best "whats the point in having all these super expensive ninja if you don't have the power and just get killed anyway?" and even if it could be interpreted as kinda harsh there is still truth to it.