No doubt at all that the system has prevented taxyway conflict/near collisions and runway incursions in the past. It adds that level of safety which, late at night (LGW), when you are completely exhausted, gives you a great deal of comfort. On the down side one could argue that pilots have too much faith in the system and therefore they relax too much during the taxy phase but I feel that the advantages far out way this.
The occasion when the GMC operator is slightly slow to respond to changing the sequence and an aircraft encounters an unneccessary stop-bar is easily rectified within seconds by a gentle enquiry and a little patience!
Far better than writing of two hulls!