ChrstphrR,
Glad to hear your still playing with stuff. I haven't had the time.
I'll give you some more rule of thumb information. Going from one core to two cores gives about a 60% boost in speed running CFD code. Adding a third core gets you about a 25% boost over that. Adding a fourth core gets you about 10% again over that. The reason for this drop is the cores compete against each other for memory access. Larger CPU caches help a little. Faster lower latency memory helps more.
If your simulation needs more memory than you have and starts to swap to disk its best to have one swap file located on each physical disk in the system instead of one big swap file. A permanent swap partition is marginally faster than one created in your root directory.
As far as setting up openfoam for the masses there is a project that has done so.
Greenpower VWT - Greenpower VWT - Virtual Wind Tunnel
Greenpower VWT
They state that their results aren't very accurate but that is what you get when you do CFD with a dumbed down interface.
Good luck