This stuff probably doesn't matter a ton in the big scheme of things, as long as there is sufficient airflow to support the engine. It's highly unlikely that these 4-cyl cars are ever going to fully utilize the flow available from the factory head, and simply cause more turbulence in the port. On a PFI car, this should be beneficial to a certain extent, helping to mix the fuel in the charge. On GDI, I doubt turbulence has much effect since the air is not transporting the fuel.
I'd be more worried about a nugget of the carbon wedging between a valve and a seat more than airflow impediment. It will, however, cause higher intake valve temps from the insulating effect. If I had a GDI, I'd try a Kreen vacuum injection clean before I took the manifold off.... or pull it and take pics like the OP did, run a pint of Kreen through the intake ala Seafoam method, let it sit for 30 minutes to dissolve some carbon, repeat with the other pint, then after restarting immediately go take it for a couple heavy-load redline trips to let the airflow suck the scum off and burn it. Then, remove the intake again and take some after pics. I'm willing to bet it will clean most of that garbage off... for sure the stuff that needs to come off!