It's always good to focus power because no matter what the meta is/changes to, you will always have your power. The thing with focusing ninja is that they can be nerfed, buffed or new ones come out and change the whole meta. You have Roshi and a solid team to back him, but you might wanna start collecting for some event ninja like Edo Deidara/Shark Kisame or you can just pull GNW treasure. I wouldn't spend coupons on seals though unless you want to. You should be getting seals from SWB since you say you're getting ranked 1-3. There is somewhat of a threshold though, like once you get to lvl 5/6 magatamas, it takes a lot to upgrade them further. Same with refines/charms. Your power is really good for your level, so it might be time to focus on slowly collecting frags for the good event ninja.