The 20 year comment is very telling and most attractions built for the large theme parks have a 20 year life. What makes that important is liability, when you design the attraction or vehicle you have to "prove" through sound engineering practices that your design is safe (typically achieving a specific SIL or Performance Level rating depending on which standard your using). You do all of your math based on the lifetime and that heavily goes into your material uses for fatigue, stress, etc. A big part of the math relates "undetectable failures" which typically aren't technical but material and things like stress microscopic fractures, metal becoming brittle, etc. Once you surpass the planned life you can not longer mathematically prove it is safe, at that point if there is an accident your liability is massively increased because you can't go back to engineering to prove you tried to make it safe, the ambulance chaser can claim you were willfully negligent. Additionally the manufacturer is now off the hook because you went past their design statement of work. Of course this is true ONLY if the monorails are past their design life, and I don't think we know that. On the subject of regenerative braking for energy, in today's transit world you don't need a third rail, the "recovered" power is sent by on the same rail that provides the power. Typically the capacitor banks are in the traction power substations. 100% of Phoenix's light rail system makes extensive use of this technology and Dallas is adopting it. Disney would be smart to replace the traction power substations anyway, they are currently using 6-pulse SCR power stations which have lousy power factor, if they switched to a 12-pulse thyristor system they would easily knock 40% off their usage (look at Phoenix, Dallas, or Denver to verify this).