1. There is some small amount of front end lift. Moving non-essential parts from front to rear also lightened the front and contributed to lift.
But, as Dick Shine proved with his track Golf Mk 4, some front lift balances better the nose-heavy chassis of the Golf Mk 4 / Seat Leon Mk 1 / Skoda Octavia Mk 1 / Audi TT Mk 1. In fact, Shine Golf Mk 4 is raised by the front a ridiculous amount, maybe 2 inches taller than rear. Something like this can't be done just with aero mods.
2. The more aerodynamic a car is, the more vulnerable to side winds at speed it will be. Aero vortices around "brake" the car in a straight line, but they also "brake" the side to side movement in the wind. Track cars have miserable drag, Cx over 1.0, they are designed for downforce, not straight line runs.
In a road car with just undertrays, spats before wheels, sealed body gaps and sealed non-functional holes in the front, instability in side winds is too small to matter. It takes a bodywork like a
Tatra T77 to become dangerous.