As someone who's worked at all three stations, I can lend my two cents.
Many many many years ago, when Disney was using the Mark IV trains, there was a door for every row of seating (5 per far) and they were manually operated. At one point in time, different cars represented different destinations, so they had different queue lines for everything. Then came the modern Mark VI trains with the bi-parting transit style doors, and everything was reduced to one queue line.
The Grand Floridian used to have one of the larger queue lines, however, 3-4 years ago they took down some of the gates to make the station look less cluttered. Only once did I ever need to use those extra gates, and that was because of a delay caused by a large technical difficulty.
At the Polynesian, the queue area is actually quite small. There is a part that extends to the front of the train, but 99% of the time, that is roped off. The only time I ever needed to use that part was back when religious services were held at Luau Cove.
As for the Contemporary... thier queue lines get used on a regular basis. Some times during the morning, but mostly after Chef Mickey gets out. Also, during holidays after religious ceremonies, the full legth of the platform will be used for a queue line. In fact, there are some times when they will also load on the Express Monorail from the Contemporary. The Contemporary queue line is designed with multiple different load zones, so that the platform attendant can divert guests multiple different ways to help with the flow.