AnooooOH, I know you're looking for a simple answer, but I don't think there is one.
You say you want "more stability" and don't want to loose "traction". But it's not that easy. Where/when do you want more stability? Autobahn blasting? Fast corners? Slow corners? It all depends...
If you want more "Autobahn" stability, you're probably fine with a conservative alignment. An alignment can make a big difference in how the car feels. For long sweeping Autobahn turns, yes, maybe swaybars would help, but I'm not sure they'd be my first choice.
What about traction? Do you ever loose it? Doesn't sound like you do. I highly doubt that any suspension mod that you've mentioned so far (swaybars or no bars) will make a significant difference for daily driving. A rear swaybar will show it's effect the most on tight turns on mountain roads or other aggressive, fast, tight corners.
Regarding tires:
A square setup is the best choice in my opinion for a good balance and quick turn-in on our cars. Note that "good balance" is not the same as stability. A naturally under-steering car will always feel more stable than a well balanced car that's ready to turn.
If I had to start all over again I'd probably do this (and in this order):
1. Proper tires (Dunlop Star Specs; Michelin PSS etc.); 235 square probably
2. Camber plates and sportier alignment (note that this is for better turn-in; not stability)
3. Springs
4. Front swaybar
5. All 4 rear sub-frame bushings
Note that the swaybar is 2nd to last in that list....
Unless you've already done 1-3, I'm not sure I'd bother at all.
Now again, my goal is a well handling car, not a rail cart
If you're so bent on swaybars and can't make up your mind. Why not get the front first, run that for a while and if you don't like it, add the rear swaybar later down the road. Who knows, you might end up saving a bunch of money that way if you decide the rear bar isn't needed (which most of us think here)...