Depends on how you want to fly.
Mouse is fine if your using a 3rd person perspective, but if you want to be in the flight seat then the stick is just so natural.
Is it worth it, I think it is. I personally have the x65-f, And I've owned hotas cougars, and X52's as well as a lot of cheap sticks. The quality change in sticks alone is insane. A cheap stick is like a $2 mouse, A better stick is more like your $50 mouse, whereas the top end stuff is a full metal naga. More buttons, less moving your hands, better ergonomics, metal instead of plastic.
If your not using your stick for more than a few hours a week then a cheap one is fine. Once you make that transition to a few hours a night then all of the above factors make the stick worth it.
There is also another train of thought regarding star citizen directly.
They plan to implement 6DOF flying.
That means
Yaw, Pitch, Rudder
Throttle, reverse throttle.
Slide left/right, Slide up down.
You don't need to map all of those directions, you can fly on 2 axis on a mouse with keys to roll, and keys for throttle. The Xbox controller cannot do as many axis and commands as a basic stick. You will always have to make a compromise with it. This is because you only have a certain number of fingers in key locations to actually push buttons.
Take a dogfight. Whilst moving about, you need targeting, shield balancing, guns, missiles, bomber targeting, countermeasures, and power management. You only have 4 buttons at your fingertips with the controller, and you have to stop turning to use the other buttons, making you an easy target.
A basic stick on the other hand. 1 hand does all the movement. You still have the thumb on that hand to operate 5 basic buttons. That's targeting, shield balancing, countermeasures, missiles, and target bombs. Your trigger finger still does the guns. Your other hand can now control the throttle and 4 buttons on the base of the cheap stick. Meaning you already have 3 spare buttons, and you can make one of those a shift key and double up on all commands, before you even have to look at the keyboard.
When you start to go up the pricing for sticks aside for build quality you also get better ergonomics and better button placement. 5 buttons on the top of the stick becomes 17, dual stage triggers, pinky triggers. Then the throttle unit does the same, your throttle + 4 buttons becomes, dual throttle + 20 buttons + mouse and scroll wheel. So you spend less time off your buttons in a fight.
If I had to pick 1 budget control system it would be stick and keys tho. In a flight/space sim expect to need a lot of commands. And expect to need them all at the same time!
This is a typical space sim keys layout.
So don't feel like it's a wasted component. Just put your regular mouse between the stick and throttle in case you need it for menu's. 
. Damn, I've spent too much on this game heheh.
Went into the updated Hangar, looking for my new toy, and waaaaaaay at the other end was this little model on a stand. "Drake Cutlass" 
