I have never read any of the supplemental books for AD&D 1E. I have never read any other edition after 1E.
I don't feel the need to honestly. With all it's quirks and gygaxisms, 1E has yet to be in any way limiting to my creativity and personal expansion.
I see 1E as "the" Homebrewers edition. It is left to be flexible so that one table at a time, each DM is able to interpret, create and adjudicate in a way that best fits them and their players.
Now, having said that and never having read the other editions, that doesn't mean a whole lot.I've read of the others and had discussions about them with folks online, etc... none of which is the same as having read/played them myself.
Now, I know that some of the methods I use in my game are supposed to have come from Unearthed Arcana. I have never read UA so I don't know that personally. I do know that some folks have told me that what I describe doing is something in UA.
I know that I have borrowed some things from posts in online forums that I later was told have come from supplemental books like UA or MM2 or even d&DG, etc...
Because I haven't read any of these supplemental books or other editions, I will not put them down. I don't know enough about them to say anything about them in that manner.
OSRIC has come along and added a new dimension to the game for me. At least in terms of creativity and sharing my creations with others. It doesn't really change anything about 1E as a game. What it does is allow me to post my new creations for the game online and others can use it if they like with no legal worries or hassles.
So for me, OSRIC isn't a supplement or Simulacrum as much as a new Appendix or something. It's like a re-statement of 1E with a way to publish new creative writing for the game.
Will I ever look at newer editions of AD&D? Probably not. Will I ever read or intentionally use material from the supplemental books of AD&D 1E? Perhaps eventually.
The way I see it, why fix what isn't broken.