Jutsu doesn't work that way. You seem to be getting destructive power of jutsu mixed up with characteristics.
I.e. Rasenshuriken has powerfull destructive jutsu, but what if Naruto needs a defence. Take Itachi, he has Sasuno to defend him from Sasukes lightning strike, if Naruto was to summon a toad to protect him from the same strike he might need sage arts to augment the defensive capability of the toad. Either that or Naruto dies.
Take Genjutsu, there are ways of defending against Genjutsu and Naruto isn't particularly good at using Genjutsu. Wouln't it be usefull to augment your Genjutsu powers when fighting against Pein in order to overcome his defences.
Take Taijutsu. Won't Senjutsu improve naruto's speen and strength proving usefull in hand to hand combat?
Take stamina. Senjutsu would improve the power of his jutsu meaning he has to use less of his own chakra. NAruto has good stamina but since when did extra stamina do anybody any harm.
Imagine if Naruto made a frog summon, wouldn't it be usefull if he could bolster the destructive capacity of that toad. Take his fight against the shikakku for example. GAmabunta could barely keep up with the raccoon. Now imagine if Naruto could use Senjutsu to aid him.
Finnaly don't forget that senjutsu does not mean simply giving a power up to your jutsu. It also means learning new Jutsu i.e. toad oil blast or frog summons, and God knows, Naruto is in desperate need of new jutsu.