There are two prongs, in my mind. The first is the immediate financial benefit of releasing software on mobile.
This includes the potential profit based on the revenue generated and the work the goes into making or porting the games.
The second prong is more complicated because it does with forecasting certain factors. Some of which include, quality assurance and the costs of doing properly QA on more platforms, extra QA for porting to mobile platforms. Pricing comes into play also because the licensing fees they avoided on their own platform is actually being reversed and paid out to the mobile platform holder. Then there is the issue of price of software, and then Nintendo software would then have multiple price points and the behavior of consumers would be harder to predict here. But it definitely would make people less willing to pay for a $60 console game.
Ultimately, even if you consider a Nintendo Mobile division as producing a consistent and reliable cash-flow, I don't think that it positively affects their total operations.
I haven't provided numbers, and the only ones I possibly could provide right now is simply the size of the iOS and Android games market compared to Nintendo's revenue for the last 5-10 years.