The consumer unit/fuse board shouldn't do much harm.
The fact that the router is inside a cupboard would be more of a problem; it's one more wall for the wireless signal to get through.
Is there a lot of wifi around you? eg neighbours? If it's congested you can suffer from collision quite badly.
You realise that not all devices can see that?
I don't know why people mess with this stuff. 1,6,11 thats all you need.
You said removing faceplate and connecting to the diagnostic socket fixed it, surely that means it's the faceplate filter that has degraded not some mystical demon behind your walls.....