I like the lowered ceiling route, have done that a couple of times in my hoses, to hide re-routed heating pipes and new cabling for lighting, so that can be a good solution. Getting the cables up there is less easy, if you want them hidden. Maybe on one wall, build a false stud-partition wall and cable up the back, like the hidden wall-mounted TV cabling ideas. If you can choose whichever wall to do this, then the room that backs onto it can use the same route to get cables up to the ceiling, by drilling through the wall at the bottom, at back of sockets, and then drilling back through above what will be the new finished ceiling level...two holes instead of chasing all the way up the wall?