As a former Disney Transport cast member, I shall chime in. For those of you who might not know, I spent 4 years in Disney Transport as both a Monorail Pilot and a Bus Driver.
Do I think it'd be a good idea to expand the monorail system? No. In fact, it would make things worse. Why you ask? Logistics! Property wasn't built to handle it. Traffic Flows are completely wrong for what a fixed guideway system does best.
Unlike most major cities, Disney has very unique transportation needs. It requires an extremely flexible and dynamic system, able to change at the drop of a hat. It also is required to be extremely simple to understand, and minimize all transfers.
-- Fixed guideway systems are NOT flexible. Disney Transport *REQUIRES* flexibility in transporting our guests. Fixed guideway systems may work GREAT in urban environments. Disney is not one of these places. We need a system that can expand and contract to current guest flow, and can be re-routed at the drop of a hat.
-- Expanding the monorail system would cost $600m to one Billion dollars. Not cheap. $65-$110 million per mile for track, not including switches or stations. $25m per train. It adds up quickly. Wouldn't we rather have a bunch of new e-ticket attractions?
-- Monorails are non-revenue generating. There would be zero return on this enormous investment. People do not come to Disney for the sole purpose of the monorail. No, really... they don't.
-- Guests want a DIRECT (and preferably NON-STOP) mode of transportation. Quite frankly, the majority could care less if it was monorail or a bus, as long as it was DIRECT. Transferring is really not an option. If you had expanded the monorail, guests would potentially have to transfer once, if not twice. That's the problem with a fixed guideway system. It works in an urban environment, because people live there, and have time to get used to and learn the system. Not at Disney. I can't begin to tell you how BAFFLING the transfer from the Resort monorail to the Epcot monorail is for many guests. They don't like it, and many would rather have the direct bus which would require no transfer, and would be much faster.
-- If one were to expand the monorail, one would want to service the highest of the congestion areas, ie: Value & Moderate Resorts. That would mean increasing the low priced rooms to a point where they would no longer serve as the great value they are currently. Park to Park travel is not great enough to warrant any expansion.
-- Walt Disney World properties are NOT designed with monorail expansion in mind. You can't just plunk down a monorail station just anywhere. And, you can't have stops as close together as you can with a bus, thus requiring guests to walk further than they already have to. Guests don't like that.
-- Diesel engines put out 80-90% less pollution than engines of just 5-10 years ago, and even newer diesel engines are even cleaner than natural gas burning engines. Newer engines get 4-5x the fuel economy as well. They are rock solid reliable, cheap to maintain, and last forever. Monorails are expensive to maintain (due to proprietary parts), and the pollution is just at a different site -- the Power Plant. (On a side note, Diesel/Electric hybrids are a great idea, but it is still in its infancy. In 5-10 years, I'm sure they will have been improved enough to be placed into heavy duty service)
--If a Monorail breaks down, the whole system is shut down. No one can pass the problem train. Hundreds of guests are inconvenienced. If a bus breaks down, it is quickly replaced by another bus. No other bus is inconvenienced. Oh, on a side note, on busy days, buses have to supplement the MK Express Monorail because it's so overcrowded.
The bottom line is this: YES, the monorail is cool. We know that. Is monorail expansion right for Walt Disney World? No. You may not like the bus, but they are currently the best way to get around Walt Disney World thanks to thier incredible flexibility. By the way, there are lots of folks out there that LOVE the bus, especially children. I used to get families on my bus all the time that just take a round trip on the bus, because thier kids want to go on one last bus ride before going home.