I have 997 turbo with giac software , tubi excaust , and evo headers. I am considering buying a plenum, and evom recirculation valves, do these two upgrades add any power?

I would suggest the plenum by IPD. I have the valves on my car and they do not do anything. In addition, you would probably notice more by going with the Fabspeed intake kit. I will shoot you a PM.