I already own a Vita, so that doesn't factor into the cost.
Also, I'm not going to downgrade my GPU when the one I have is already getting close to the limits on modern multiplat games. To get a graphics card that's at least comparable to my current one (a 470) but that can also stream to Shield I'd have to get a 660, which is ~$200. And given that current gen games are stressing my card I imagine next gen games are going to quickly outstrip its abilities, which means to keep pace and play the next gen games I'd actually have to spend even more on a card.
Plus there's the whole not-all-games-are-supported thing.
Even putting all of that aside, paying $200 for a card that's just comparable to the one I already have doesn't sit well with me.
I will surely upgrade my graphics card at some point, but now is not that point.