i, personally, would say playstation TV isn't a good replacement for vita.
1. not ever vita game is supported
2. the controls are remapped so (i assume) not every game will play "like it is suppose to"
here is how i see playstationTV. it plays some* vita titles. some psp titles. some ps classics. some ps3 titles (via psnow). and i imagine in the future some ps4 titles. ..and, of course, the most popular tv services.
for a more casual player playstationTV is a cheap way to get access to a lot of content. experiences won't always be optimal but casuals probably won't mind. for the more "core" player that has to have access to every game in the highest fidelity and in the optimal configuration,.. there is ps4 and psvita.
personally, i think sony was foolish to ever market it as a psvita. i think it should have been an entirely different product with an entirely different OS focused on what it is. an inexpensive way to get to a lot of content to those that don't care about all that "extras" provided by ps4.