Ok I have been there done that. yes - Factory VT rotors are often crap. I when to a set of GSA slotteds all round and that helped. Change PAD spec as well to pads that cover the entire metal plate rather than just a smaller one. Because of the sometimes less than stellar quality of the meal used in the original pads, you can get parts of the rotor heating unevenly - heat not being conducted away evenly in spots. GSA has some police spec pads that rock.
Things you wouldn't normally check - make sure you DON'T have a unidirectional tyre mounted backwards on one rim. that WILL shake one corner all to hell.
Make sure your pistons in the calipers are moving freely and equally - a casting dag can limit travel on one cylinder.
For gawd's sake NEVER EVER EVER let a lazy tyre tech use a freaking rattle gun on your wheel nuts. The studs on VT's are soft, designed to give rather than shear. Over tightening will stretch a stud. The ONLY safe way to do up a wheel nut is to nip it up by hand with the car off the ground, with a brace, then LOWER the car until there is some (not ALL0 the cars weight on the ground, and tighten then up with the brace. Do not really lean or swing on it. Just tighten. This is for TWO reasons - Firstly, it will be you or the missus that has to undo these nuts on the side of the road when you get a flat and Secondly to avoid stud stretch.
Stud Stretch will make the disk assembly unbalance and exacerbate any shake issues you have.
If you still have brake shudder these are the steps I woyuld take, and in this order -
1. Get wheels balanced. All of them.
2. refit Balanced wheels by hand using above method. If brakes still shudder -
3. Check tyres for worn spots indicating bubbles in tyres. If all good -
3. replace Brake pads with GSA Police spec pads. All 4 of them. If they still shudder -
4. Replace rotors with slotteds - NOT RDA brand as they have has some quality issues. I use GSA and they are great. Again - all 4 of them.
5. Replace bushes and rose joints in the hub mounts, and the trailing link bushes ( i can't think of the proper name) from the front chassis rail to the hub. If it still shudders -
6. Throw the car away.