The only reason you would want the evo ecu is for the ability to use ECUFlash to change fuel and timing maps..etc. It wont add power in itself. About the swap...

Its not plug and play. But its not hard either. Basically what you need is an evo 8 4 plug ecu. You swap some pins around in the plugs on the chassis side per the wiring diagrams on tuners. Its just a few, I think the fans and the fuel pump relay are the only ones that really matter..after that you reflash the ecu with a tactrix/evoscan cable to delete the imobilizer, change injector/maf scaling to fit the 2g...

As far as money...it costs ~$100 for the cable and $150 for the ECU. Thats more like SAFC2 territory John. Although hanging out for an hour in the passenger footwell isn't fun

Just go to dsmtuners.com and check out the engine management section. Theres a pretty good 10 page thread.