What do they add for being a console maker?
Quality control at a level worth speaking of? Maybe in the NES and SNES days but nobody wants to go back to the stranglehold there. Today the Nintendo seal is a running joke.
Controllers? Sure I guess they have the nice dpad still, though I hear the final patents will expire soon and most have already. That said I can't imagine there are many for the glory that is proper push button switched controls and nobody seems to make those right now.
Hardware like the dominant platform (nowadays the PC)? Again back in the NES and SNES days it offered something over the PCs and minicomputers of the day (actual scrolling, whoo)
Being a joy to work with? Hardly.
A reference grade service in anything? I already dissed their online offerings, their OS abstraction stuff (MS and sony handling chat and the like far better, Nintendo then giving rise to the whole splatoon thing)
A chance to work with some great IPs? I guess they have loosened up a tiny bit but we are not going to see them unstable any of the big guns any time soon.
A chance to get a mega game funded? A console exclusive for Nintendo is not really a draw these days, and less than that of Sony or MS. You probably won't even get some marketing on the cheap for being on Nintendo gear.
A chance to get in on a potential big audience mega cheaply? What with Android in the world?
The only thing I can think of is they still have a thing in the minds of some to be "family friendly", whatever that means. Such a thing could matter but if you were a greasy teenager in the US when the NES hit we are not far off many of those possibly having grandchildren ( Mother's mean age at first birth: 25.6 (2011 est.)
https://www.cia.gov/library/publications/the-world-factbook/geos/us.html ) so games are hardly an unknown. I will give that though Sony and MS could possibly have cleaned up here they seem not to have, no idea why.