Yes, it's often just as simple to run an external Ethernet cable. The BT Infinity "Data Extension Kit" is more or less that.
This week,I cabled from a router to a back bedroom/study of a professional photographer, and saw speed go from 1.6mb down to 16mb down.
I'm frquently amazed that ADSL works at all. Likewise wifi. All over a single pair of 0.5mm copper wires which hang off poles, sit in damp street cabinets, and are subjected to all kinds of interference.