Cat or Caterham Cams are more aggressive, but as stated they are super expensive and are a lot of work to get them to work properly in the car.
Other than that, the SVT Cams are equivalent to a Stage 4 Cam for the standard Zetec engines. No one else has better cams for the SVT other than the Cat Cams.
A Tune would be your best option.
Now if you are thinking about opening up the cylinders some, looking into ITBs, getting some steel valves and stronger cylinders ... then sure get the cams. But if you are only wanting to get more HP for N/A without spending much money, forget the Cams.
Tune, CAI, Short-Throw, Dog-Mount, Stiffer Suspension and an ORP/HFC and you will be quite happy with the ride. It's not about HP with this car, it's about driveability and automotive course performance.