This is perhaps overdoing the need for some sort of themed travel experience. On my one trip to Disney World with my wife and 8-year old daughter in 1999, we stayed at the Wilderness Lodge, and, except for the boat ride to the Magic Kingdom, we relied on the Disney buses to get us places. Yeah, we took the bus to the ticketing center to ride the monorail to Epcot, but when we needed to get back to the hotel later in the evening, the direct bus was fine. What's important is the buses are frequent and go everywhere.
Whether they need a fixed guideway from the Virgin Trains Station to the parks really depends on how bad the traffic is, and whether the buses get caught in the traffic. What travelers would really want is a single seat ride from the train station to their hotel or directly to the park, if they're day-trippers. It d0esn't really matter whether it's a bus or some sort of fixed guideway gadgetbahn.