While I do think people are calling the PSVita a failure a little too quickly, I don't think it will have as great of an impact as a Nintendo handheld (a little too obvious, I know). Nintendo has been the undisputed handheld kings for over 30 years (If you count Game & Watch). They didn't have a serious competitor, for over 25 years, until the PSP was released. And even then, the DS more than doubled the sales of the PSP.
I don't think this will change any time soon. The 3DS already has a +10 million units headstart, and it looks like the PSVita is targeting a narrower market than the 3DS's market (especially when you factor in the price).
Switching subjects, Nintendo isn't even worried about smartphones...at least for now. Iwata gave a speech last year about how smartphones and dedicated portable gaming will probably never be on the same level. And it is showing!! People who play games on iPhones are looking for something cheap/free and something like Cut The Rope. Nintendo 3DS sales in year one are even more impressive then what the DS did in its first year. So, it doesn't look like smartphones gaming is deterring people from investing in portable gaming machines.
However, tablet gaming is another story. Tablets aren't competing with the 3DS/PSVita, but Nintendo feels like they can capitalize on tablet gaming in home consoles. There is a reason why the Wii U controller is a tablet. Maybe Nintendo feels that iPads are a bigger threat to gaming consoles than iPhones...