Well... there are some reasons for why they extended the life on this series. Primarily it's because they were doing all the automation work. I'm sure they didn't want to order the new trains until the automation experiment successfully finished and they could incorporate it properly into new trains instead of it being add on extras. Second, they were able to cannibalize the crashed train for parts, which definitely extended the life of this generation. And finally, as has been pointed out on other threads, there is no off the shelf solution. The beams are the wrong size and, I believe, draw the wrong current, for any modern replacement.
So while I agree that these trains are well past their sell by date, there is good reason why Disney has tried so hard to keep them in "good enough" running condition.