Nothing.. i would recommend if you hv an engine head with 4valves per cylinder.. rather tha 2valves per cylinder...which means 16v at least, since it will dramatically improve airflow in n out of the engine,thus improve power..
then if u wanna cramp in more air with an FI bolt on, it would not be such a waste.. superchargers are expensive mod.. with ur current engine 2L 8v.. i bet the result is not as much as what ull b paying for.. either u have the Sc custom from other Sc Engine to fit urs... or u get imported Sc specially made for the VW Mk4 which will cost a lot for little power..
Turbo charge bolt on would b a cheaper option, but with minimal boost so that u dont blow the engine with stock internals.. but still enjoy the extra power with minimum reliability problems..
i guess ur using a VW golf mk4 rite? keep on studying what options u hv for ur ride which best suits u bro..