I play a lot of Lissandra and I feel that she is fine the way that she is. The range on her q is almost double if you actually hit something. Putting the slow on the whole q damage area would break it. You could slow 80% of the enemy team for the entirety of any good team fight. Also considering the damage and Lissandra's passive increasing the range would make Lissandra too much of a power house in lane. Now she can recieve great ganks. Have long poke that you can get for free. Here let me just smash Gragas into the already existing Lissandra kit.
Also I don't view Lissandra as an entirely utility mage. The has alot of cc. No doubt about that. Between her and a Leona you can lock someone down for a looooong time. But Liss also brings quite a bit of damage. Her disadvantage is her short range. She can't do a long range burst like a Xerath or lock someone down from a distance like a Lux. Which brings me to her E. Her E is perfect in my opinion. It is one of the if not the longest range non ultimate teleport. Its low damage is keeping her in synch with her short range kit with a long range teleport. Putting more damage on it would be very similar to what I said earlier about increasing the range of her Q. Once you combine lissandra's passive with it would give her a long range poke for free in lane. The slow travel speed gives her great juke potential. It is slow enough to let you juke but fast enough to be useful in over a thousand ways. It provide some good counterplay if you can get some cc on liss and it also allows her to zone pretty effectively. I have never had an issue getting the initiate in a teamfight. in that 5v5 clam before the storm everyone is so on edge that you can either get it in before they realize what is happening. Another trick i have learned is to use Glacial Path to go in and instead of popping the root or anything like that just immediately use a zhonya's houglass. You will most likely be able to bait out a lot of cooldowns and mayber a couple ultimates which can then allow the rest of your team to safely charge in. In my personal opinion her E is perfectly balanced. If you increase the damage it pulls away from its intendeded utility, if you lower the cooldown you now have a champion that can travel across any barrier on summoners rift almost at will, if you increase or decrease the speed you interfere with the the very delicate balance that i feel that riot has pegged on the head.
Finally we arrive at her ultimate. Again i argue that this is a perfectly fine ultimate. The damage is a little low when you look at it until you remember that everyone in the area of it takes the full damage and pretty much everyone recieves some crowd control. a 20% slow is all a team needs to be at a disadvantage in a team fight. Not to mention the stun which is oh so handy as it is a point and click instantaneous 2 second stun. I can't think of another champion of the top of my head that can do that. It is always satisfying to drop a lissandra ult on a katarina as she starts her death lotus. Now my second arguement is that Lissandra has essentially two Ultimates. If that isn't utility then i don't know what is. Which is what you were saying Lissandra should be right?
So yeah, I'm sorry about the essay that I wrote. I was bored and sitting in class. Please feel free to post your comments/rebuttal/etc.