Yep, exactly why it's so noteworthy. It won't singlehandedly send Vita into the sales stratosphere (or even necessarily a >20K weekly baseline), but potential-sales-wise, it's arguably the biggest game announced for the JP market to date, and possibly not by a narrow margin either (it's tough to predict exactly how much GE2 PSP will eat into the Vita version's pie, post-Toukiden).
I'd guess that GE2B/GE3 and Toukiden 2 are more likely to be PS3/(PS4?)/Vita than exclusive, given other announcements from their publishers, but the latter is possible.
To me Phantasy Star along with the microconsole basically represents Sony managing to do about all they feasibly could for Vita owners at this point.
The device isn't going to looked back on as some stirring success, but it should be able to live out at least a near-normal life cycle given it has content through at least the end of 2014, and thus the momentum created by that should support it through 2015 or 2016 in Japan, albeit at a rather low baseline.
To me, the main question is where they go from here. When we were sitting halfway through the PS3 generated, the obvious answer was "Well our core idea seems to be working, but we need to get costs way down for both consumers and ourselves, and make out platform way more developer friendly."
For the Vita, I don't think there's an obvious next step. I do see a couple of possibilities, but don't know which they would choose:
Option 1.) Try to convert what they can of the Vita supports into PS4 supporters and cede whoever doesn't come over to other platforms.
Option 2.) Make the microconsole the flagship device for their next "handheld platform" and then sell a "portable version" of it in Japan and maybe at specialty retail in the West.
Option 3.) Make the microconsole with portable version, but base it directly on Android so they can get all the content being made for Android phones/tablets/microconsoles along with content specifically targeting their device. They might somehow be able to work in a sandbox mode where developers can call lower level PlayStation APIs to get more juice out of the system if they need it for exclusives or to ease development for games that are ported across the PlayStation ecosystem. However, it would use regular Android mode for most things.
I'm excluding "continue on as is" since I honestly don't think that's a remotely logical idea given how this generation went, though I guess it's not entirely impossible if they're crazy.