MG13 (Hi, MG13!) is correct that "purist" is mostly used as a condescending put-down.  The reason it's a put-down is that the conservative's motives are questioned.  Oh sure, they say they are honoring the Imagineers' original intentions, and they say it's always a bad idea to fiddle and tamper with an acknowledged masterpiece, even if the motives are good, but in reality the "purist" is driven by emotional immaturity.  They are nostalgic to an unhealthy degree, expecting everyone else to cater to their childish need for everything they loved in their youth to remain exactly the same forever.

The plaque thing is a good illustration.  No one with two functioning brain cells would argue that the Imagineers consciously and willfully intended those plaques to remain a burnished gold color forever.  It they did, periodic polishing would have been written into the maintenance manuals.  More likely they didn't give it any thought at all, assuming that the bronze would do would bronze does.  If they did think about it at all, they may well have assumed this would be a good thing, adding a sense of age to the house.

The OP assumes that any change at all is objectionable to the "purist," whether effected by an idiotic WDI team or by Mother Nature.  The first of those angers the nostalgist, but both of them grieve him.  A "purist" who is motivated not by nostalgia but by a respect for the art and the artisans who created it may likewise be angered by changes due to an inept WDI team, but he is not bothered by the second kind of change unless it's a question of poor maintenance, of letting the thing deteriorate in a way that no one would approve.  I know of no one who thinks the lush growth of the trees around the DL HM is something to be regretted.  That is in no way inconsistent with disgust over unnecessary "improvements" unless you assume the "purists" = "childish nostalgics," despite their protestations.