In my opinion, Sage Nardo is NOT worth spending seals on just 'cause of the high chance of getting Ao or Traitoro.

However, he IS an extremely solid character (one of the few who can simultaneously play the role of a Tank and a Damage Dealer on a team) and you should shoot for him in events. In the past he's been pretty decently easy to get in the past, so you can probably amass fragments of him from there.

The thing we have to think about here is the overall * for buck when it comes to spending seal scrolls. Spending on Sage is like a really high risk high reward type of thing in that if you don't get him you practically just wasted your scrolls. I don't like that type of thing so I wouldn't rec it, but it's all about preference here.

If you spend in something like either Jinchuriki or 5 Kage, you at least have a chance to get solid characters like Mabui, GNW Tenten, et cetera from the commons. In Sage, all your commons are easier-to-obtain characters like Jugo...