Well, I don't think his ultimate should offer more than what it does. I mean you could say that for about a bunch of champions in the game.
I think if you were to give his ultimate more, it would just be overloaded.
For example if you let him attack the player when he ults them.. It wouldn't be healthy. I mean his ultimate is quite lengthy on the player he is ulting.
As for his Q. It's actually good, not sure why people don't like it.. I hope you have used Triforce (I honestly dont know if you have used Triforce) cause to me, when I get Triforce, that Q damage becomes insane cause the sheen proc after the Q or whatever just does awesome damage.
His W is decent. I like that it gives him a massive speed boost and resistances. Can get around the map in a breeze and surprise people, especially if you control crystals.
His E is the only ability I think that could be reworked really. He shoots it too slow, but it sets up his stun if he hits you with it, and slows you. I think he can possibly shoot it faster and be good. Maybe increase the damage it does just a bit cause it's a little weak.
I kinda enjoy Skarner the way he is, I mean I got a mastery 7 skarner too (well if I spend my blue essence on him, already got the 3 tokens). I got about 60k+ experience on him, so I can say I definitely play Skarner and at a pretty good level.
To recap.
If I was to buff him. I would change his E to shoot faster, possibly do more damage.
Maybe do something different with his Crystals and passive. Skarner is at his best when fighting inside a crystal he controls.