That's definitely simpler! 

Had to use 

10-_.countBy

instead of 

9-_.countBy

since it gave the wrong count for me.

lol forgot about swamp... code updated

Here's a bit of code I came up with for getting how many creeps I can have 'harvesting' a source simultaneously:

function Get_Connections(source)
{
    var result = [];
    var North = source.room.lookAt(source.pos.x, source.pos.y - 1);
    North.forEach(function(object)
    {
        if (object.type == LOOK_TERRAIN) 
        {
            result[0] = object[LOOK_TERRAIN];
        }
    });

    var NorthEast = source.room.lookAt(source.pos.x + 1, source.pos.y - 1);
    NorthEast.forEach(function(object)
    {
        if (object.type == LOOK_TERRAIN) 
        {
            result[1] = object[LOOK_TERRAIN];
        }
    });

    var NorthWest = source.room.lookAt(source.pos.x - 1, source.pos.y - 1);
    NorthWest.forEach(function(object)
    {
        if (object.type == LOOK_TERRAIN) 
        {
            result[2] = object[LOOK_TERRAIN];
        }
    });

    var East = source.room.lookAt(source.pos.x + 1, source.pos.y);
    East.forEach(function(object)
    {
        if (object.type == LOOK_TERRAIN) 
        {
            result[3] = object[LOOK_TERRAIN];
        }
    });

    var South = source.room.lookAt(source.pos.x, source.pos.y + 1);
    South.forEach(function(object)
    {
        if (object.type == LOOK_TERRAIN) 
        {
            result[4] = object[LOOK_TERRAIN];
        }
    });

    var SouthEast = source.room.lookAt(source.pos.x + 1, source.pos.y + 1);
    SouthEast.forEach(function(object)
    {
        if (object.type == LOOK_TERRAIN) 
        {
            result[5] = object[LOOK_TERRAIN];
        }
    });

    var SouthWest = source.room.lookAt(source.pos.x - 1, source.pos.y + 1);
    SouthWest.forEach(function(object)
    {
        if (object.type == LOOK_TERRAIN) 
        {
            result[6] = object[LOOK_TERRAIN];
        }
    });

    var West = source.room.lookAt(source.pos.x - 1, source.pos.y);
    West.forEach(function(object)
    {
        if (object.type == LOOK_TERRAIN) 
        {
            result[7] = object[LOOK_TERRAIN];
        }
    });

    return result;
}

and its usage: 

function Assign(creep)
{
     var sources = creep.room.find(FIND_SOURCES);
 
     for (s = 0; s < sources.length; s++)
     {
         var connections = Get_Connections(sources[s]);
 
         var count = 0;
         for (c = 0; c < connections.length; c++)
         {
             if (connections[c] == "plain" ||
                 connections[c] == "swamp")
             {
                 count++;
             }
         }
 
         if (count > 1)
         {
             var connected = 0;
             for (var name in Game.creeps)
             {
                 var existing = Game.creeps[name];
 
                 if (existing.memory.assigned == sources[s].id)
                 {
                     connected++;
                     if (connected == count)
                     {
                         break;
                     }
                 }
             }
 
             if (connected < count)
             {
                 creep.memory.assigned = sources[s].id;
                 break;
             }
         }
         else
         {
             var assigned = false;
             for (var name in Game.creeps)
             {
                 var existing = Game.creeps[name];
 
                 if (existing.memory.assigned == sources[s].id)
                 {
                     assigned = true;
                     break;
                 }
             }
 
             if (assigned == false)
             {
                 creep.memory.assigned = sources[s].id;
                 break;
             }
         }
     }
}

Obviously this doesn't take into account any structures next to the source, which you hopefully should never need to.

When a controller's level falls below the requirement for operating a particular structure, the structure gets highlighted in red... but after raising the controller's level back up the structure does not come back into control (still has red highlight) until game is restarted.

[edit]

Going to World and back to the Room also resets the red highlight.