Well, we used to visit the Poly and spend some money at least once every trip to WDW. Can't say this will still be true on our next trip. The old lobby was georgeous, tropical, soothing, relaxing, and charming all rolled into one. You walked into the lobby and there was a tropical paradise welcoming you. The new lobby --- eh.
Yes, tropical foliage and water features are difficult and expensive to maintain. This feature was also over forty years old and, no doubt, had its problems or was causing problems. However, it could and should have been replaced with something just as lush and tropical even if on a somewhat smaller scale. Please don't insult our intelligence by claiming it was too expensive or it couldn't be figured out how to incorporate it into the new lobby. The water feature was the heart and soul of the Polynesian lobby. Nothing against Trader Sam's, but is it now supposed to be the lobby's main attraction?
As it was meant to,the lobby and the whole resort represented the the idealized tiki tropical feeling.. So what? Something iconic does not have to be changed just for the sake of change.
On web sites the vast majority of the responses about the removal of the waterfalls is a feeling of great sadness and loss.