That's roughly $6.6M per mile, and sounds about right for the rail infrastructure itself (beams/supports/electrical). It sounds even more credible when you consider that the original construction cost was about $1M per mile in 1970 dollars.
People are quick to point out how public monorail systems cost a fortune to build and therefore it would cost Disney hundred of millions if not billions to construct several miles of new rail. But the WDW monorail tracks differ substantially from municipal systems and Disney owns the ROW. Take a look at the support columns and beams. There are approximately 25 supports per mile of rail, each consisting of about 30 yards of concrete. The rails themselves are precast. Long story short, I think the engineer you talked to is spot on.
That makes more sense to me. I've never understood the $100-150M/mi notion of a monorail. It seems like, just by looking at it, that it should be cheaper to build than roads, subways, light rail, etc. It's support columns with a beam and power. It's always boggled me that you'd see, "Oh, building a monorail is too expensive," but then you see cities build and expand their subway systems with no thought to the cost as if it's cheaper.
All that being said, while monorails are sexier, the buses make more sense. They can funnel them to where they're needed in the case of an event or large crowd, everything doesn't stop because one breaks down, etc. They're not sexy. They're pretty boring, but they really do make the most sense.
As for the dream of expansion, which I think we all know isn't going to happen, They'd really need to tie in parks and resorts. It wouldn't be of much use just connecting parks (not that anyone has suggested it) as it's really be an expensive park-hoppers train. Connecting parks/resorts without making it suck because of all of the stops would be a challenge.
Regarding ROI, I don't know how you'd even quantify that. On the one hand it may pull in a few more people (I wouldn't guess a lot) and you may be able to charge a little more at the deluxe hotels that it stops at but it doesn't seem like it'd really pay off any any way.
Another thing to consider is that, while the loop around Bay Lake is quite nice and scenic, the line to Epcot is pretty boring. You get some interesting things to look at when you approach Epcot and go through it but the rest of it is a lot of yawn. It's pine trees and a road. If anything, you have a better view from the road looking up at the Epcot monorail as you approach the Magic Kingdom.
As it is, I think they're approaching the "better fix it or get rid of it," choice. It used to be that I'd just park at Epcot or the Magic Kingdom and then ride the monorail over to the other one at the end of the night knowing I could get back. Now I'm not so sure so I just drive between the two. It's actually pretty rare when I ride the Epcot track in part because it's boring but also because of the weird schedule that they keep with it, now.
If they keep the monorail then it seems like maybe they need to consider building a small maintenance shop over by Epcot where they can service and park the Epcot line trains without affecting the other lines with track switching. I think they're also overdue for getting new trains. I think, if I remember correctly, that they typically replace them around the 20-year mark and this current set is approaching 25 years.
If they did get rid of them people would initially complain but as the pylons were pulled up and the track removed people would have fond memories but get past it like any other ride that's been removed.
