I have a 3BG Passat, the first mod i did was to replace the springs with eibach, it lowered the car by 30mm. Could have gone lower, gee these cars have a huge gap in the tire well. Anyway as Gamba stated the eibach dramatically improved the feel of the car, I wont say it changed handling by much because springs alone wont do much. In order to get the most out of the car you need to do the shocks as well my preference is for Koni but there are other brands you can choose from. Next if not before get yourself a rear swaybar, this is a must have mod it will significantly reduce understeer on your car. Lastly get a front lower tie bar this will add rigidity to the front end thereby increasing steering response.
Oh should add I have all these mods except for shocks which are still oem. So atm I am very happy with the setup but I know I will be even happier once I replace the shocks. One more thing coilover are not necessary if you don't want ride height adjustment, they are the most expensive suspension option you can get and for most unecessary. Once installed I doubt you will bother adjusting them.
Keep it on the road.
Walter