Fallingwater's restorative issues were moreso a combined result of an outer support beam being mis-calculated (not by Wright, but by the person reading his plans) in size, as well as the lack of respect or understanding of just how significant Wright's ideas were, as people tended to live and grow in the homes he designed. Of all the houses I've visited or researched, most of them east of the Mississippi have been victim to our weather patterns and not maintained by the revolving door of owners that have claimed them (His prairie style is great for the midwest and southwest, not so much in the northeast, FallingWater being the outlier).

As an anecdote, up here in the northeast, we have two examples of FLW homes that were recently restored: The Martin House in Buffalo and the E.E. Boynton House in Rochester. At one point, the Martin House was abandoned, and left to the elements and lack of maintenance it suffered greatly. Restoration efforts started in 1996 and continued into 2008 as funding and craftspeople were available.

The Boynton House has maintained residents since EE Boynton paid for it to be built, and it too was subject to Wright's notoriously bloated budgets and lack of sticking to any one plan (Yet Boynton continued to write checks). The Boynton House's restoration was moreso the current owner's desire to return the house to how it was originally built and designed by Wright, as owners had come and gone while leaving their mark. There's even an urban legend that at one point, previous owners threw out all the original FLW designed furniture and someone with knowledge of Mission style design snatched them up, and they now sit in a local art gallery.

Ultimately, FLW was recognized for his unique approach to architecture during his time, and was highly sought after by those seeking his style, but like all things, his specific style is not timeless and the current appreciation for his contributions to architecture were not always so.