Remember my friend.We adjust sweetfx so that the games look the best on our "own" screen,It may look awesome in your screen, but it probably won't be the same for other people, thats why we should always aim to turn sweetfx off when sharing our own screenshots .

Anyways I might post some 4k screenshot tomorrow, only if you allow me of course. 

You are confusing things. Dolphin enables you to render games at a much higher resolution than it originally was. This doesn't say anything about the resolution you are actually rendering it to the screen.

Actually new age emulators which enable you to render the games at a much higher resolution internally than they were rendered on console can do a lot of wonders to many games.
Sadly OP hasn't posted really good images, in my opinion. They are way too dark.
Sometimes it can even do wonders to PSX games but in general anything from Dreamcast and above looks way better than on console and even by todays standards nice.
I shamelessly copy from a GAF thread:

PSX:


PS2:


PSP:


Wii:


Dreamcast:

Thread author please remove those misleading pics or make proper ones, yours look like crap :p

I only tried Xenoblade Chronicles, it looks amazing in Dolphin max settings - like PC games post 2005 on max settings.

Why aren't they upscaled on Wii U?

The recently released Wii VC should be at the very least.

HD is like the best thing to happen to Nintendo in a long time really.

Even "low budget" games like Captain Toad have moments where you go "wow this is beautiful".

Thank goodness the SD Wii era is over. Going to back to playing Galaxy 2 in SD was a fairly rude awakening. Still a terrific game ... but man it looks like hot garbage in terms of image quality.

Metroid Prime 3 corruption :')

Really need to play Mario Galaxy 2 and Skyward sword when I get a Wii U

Dolphin do Miracles and show how Wii games looks:

Wii U

VS

Wii Dolphin

The thing about emulators is that they are not a 'true' representation of what the native hardware(in this case, the Wii) could do. I play N64 roms and they look a million times better on an emulator than they do on an N64 even through an RGB SCART connection which is the best the N64 can get. Even a GC/Wii hooked up via component-to-HDMI cable won't look half as good as a PC monitor running a GC/Wii game through an emulator running 4XAA etc.

Go ahead. :)