There is definitely a lot of room for improvement on it. Next priority is a weapon though I think, and those are very expensive.
Yeah, I have just 12% run speed. I was nervous about dropping it also, and when I sold my lacunis I was worried I was making a mistake, but I figured I could always go back to it if need be. Anyways, movement speed is really good and it would be nice to have more, but I've found that it isn't strictly necessary. Again, yeah, trying to burst things down is the key. You do have to kite elites/champs some though, of course, and movement speed would be nice but I've found with temporal flux and teleport I've been able to do fine without it.
On a related note though I have been switching back and forth constantly between venom hydra and arcane hydra and I think I am beginning to like arcane hydra more. The total damage is lower, but it is more front loaded and it crits for high damage and it applies the constant temporal flux slow that makes having only 12% movement speed more viable.