You would lose the lovely low down grunt that the GS has. A VVT engine won't give more torque than a standard one only spread it around better. You could get more HP but only at higher rpm. The GS has plenty of go low down but runs out of puff a bit early, VVT would keep the lown grunt and allow the engine to carry on spinning up more to find some extra HP to match the opposition.
An important part of VVT introduction would be help with emissions, which is a struggle for the boxer engine, as it allows far more scope for the designers/engineers to optimise fuelling over a far wider rev range.