Oh man this seems fun, from now on all of my power comparisons will be in DBZ terms.

Vita has a mobile GPU. That kind of cards are designed with power consumption in mind, so they can't beat a desktop or console GPU of the same time frame. Current mobile GPUs can't even come close to PS3 or 360. Vita has one of the most powerful mobile GPUs, but it isn't stronger than a PS3. Vita uses it qHD screen to help when closing that difference (qHD is 1/4 of 1080p or 1/2 of 720p).

Wii U has a modern GPU, so it isn't way stronger than Vita and stronger the PS360. Of course, that isn't a fair comparison. What happens here is that Vita is specially strong for a portable and U isn't as powerful as the other next gen consoles (we only know PS4 now, but it's pretty much impossible that 720 won't beat the Wii U, since it will be more comparable to PS4 power wise).

In terms of raw power, Wii U is pretty much stronger. However, the extra gamepad screen may or may not put a larger strain on the actual hardware than the PSV screen.

The vita is less than a 360. The Wii U is more than a PS3.
From a gamers perspective thats what you need to know.

You asked the question, what are you doing answering it?

Streaming to the gamepad doesnt put a strain on the power. It uses a seperate chip for that, so it shouldnt factor.

Ah, my bad. 

That "separate chip" is still part of the Wii U though. Those extra 409,920 pixels don't draw themselves.

This is a really weird comparison to make.

A home console versus a portable?

We're talking apples and oranges.

Wii U is far more graphically-sophisticated than PS Vita, given that it doesn't have to worry about size, or power consumption reliant on a lithium-ion battery. Home consoles have large power supplies plugged into the wall, and they have cooling fans.  Portables need to have low power consumption and can't be too powerful, otherwise the components over-heat and the system is ruined.  One needs to sacrifice power and ability for the sake of battery life and heat, the other does not.

According to the logic I've seen on this site:

The Wii U has a tri-core 1.2 Ghz CPU, and a single core GPU.

The PS Vita has a quad-core 2.0 Ghz CPU, and a quad-core GPU.

That means...

OMG, WII U LESS POWERFULZ THAN PS VITA CONFIRMEDZZZ!!! INSERT NAME OF 1993 FPS BY ID SOFTWARE HERE!!!