So I've been looking at a couple of videos on youtube:
http://www.youtube.com/watch?v=TtHVhst3IZI&feature=related
http://www.youtube.com/watch?v=GX9WscML9mQ&feature=related
http://www.youtube.com/watch?v=3cGBLV8CtH4&feature=related

And while they look nice (though the third one had too low gamma and the second was way too uhm... Gray...) they look very laggy.
Are there any good mods out there for Morrowind which enhance graphics like these do, mostly gameworld and characters wise, but doesn't lag the game up?

MGE is your best bet, as it is highly customizable. You could have just a bit of distant land + hdr/bloom filters without much lag atall.

This one: http://www.tesnexus.com/downloads/file.php?id=5535 ?
Oh and I've only added mods to New Vegas so I don't know how this will work out; Do I need to create a new character for this? (Certain mods do that whole "You are about to load a save with content missing")

MGE itself isn't a mod - it's a clever bit of dll trickery. Vanilla MGE shouldn't affect your saves at all as far as I know.

Just installing MGE itself won't get you those kind of visuals though.

I recommend this guide:

http://knotstheinane.blogspot.com/p/morrowind-modding-guide.html

You certainly don't have to use everything in it. Just give it a read then play about and see what you like and what your system can handle.

Is interesting that you, by coincidence surely, have chosen 3 Youtube vids that has one of the worst gamma attenuation for Morrowind. The gamma settings in these videos are HORRIBLE.
Anyways, those graphics enhanced mods are for the most part outdated. The new kid in the block in graphics enhancement is Morrowind Overhaul - Sounds & Graphics. Is basically a compilation of the best mods to beautify MW. The author is working on another compilation related only to gameplay enhancement too.

http://www.gamesas.com/index.php?/topic/1196406-relz-morrowind-overhaul-sounds-graphics/

As for the lag, it will all depend on you rig of course. What's your specs?

this kind of thread is always a reminder to all people how good a game morrowind was.

Great games like Morrowind, like art masterpieces in the Louvre, never gets old. They are sediments with thick layers of history molded by modders whose works are slowly been rediscover piece by piece by newcomers.