i believe it is a simple matter of what niche does it aim... i mean... A serious gamer who wants to play on-the-go, might not want a graphics-wise weak system like the Nintendo's 3DS, and may be willing to pay a quarter-thousand dollars for a nice, powerful and trusted design-wise portable console.
And may i add... the game library of the Vita is actually exciting, since many great titles will be present, like Uncharted, God of War, Need for Speed (the serious ones) and many exclusives with very good graphics, which is what i think hardcore gamers nowadays want.
Just two notes i wanna make explicit.
1: i hope the Vita doesn't heat up too much, because with so much power overall, and no dedicated cooling (at least the PSP didn't had, as far as i know), which would be very troublesome.
2: if Sony downgrades vita again, i'll remove my good thoughts and start to think again about it. I was very, very excited about its very-high end specs when it was first talked about some months ago. Something like several gigs of RAM, a very high end GPU, a quad-core processor and something like that were the rumors. I was thinking "wow, finally the handhelds are catching up to the real world. Thanks, Sony." and now i'm more like "meh... just another facelift over the old PSP... some touchscreens? Little improvement over graphics? No, thanks."