I guess people do collect fakes, forgeries, overprints, and notes with defacement (stampings on them). Whether that will be a new "trend" in collecting time will tell.
I won't be betting on it.
A note with a famous person's signature on it is another matter altogether (some collectors prefer a note with some history or pedigree)
A forum member reported a 1979 "33" $5 test note stamped with "Where's Willy?" which would be collectible (since so few test notes were issued and they are --after all -- extremely rare with a unique serial #), and it apparently is still floating around in circulation (if you believe the website). I suppose every collector is different. I will take a clean pressed note (lightly) over one that's got writing, tears, or stains on it -- but it should be rare.
I put a 04 BER note that was in flawless crisp condition back into circulation before I knew how scarce even the 2004 BER notes were. But it was stamped with the "Where's Willy" ink, and to me, its only worth face value. If I had it in my collection now...I'm sure I'd be fretting about how to ditch it. Maybe that's my "weakness" as a collector -- but it hasn't cost me anything to be selective (and it usually pays off in the long run).
The "Gold Flags" will continue to be "dumped" on the internet (and sold to the uninformed). You won't see any of these sullied notes sold at shows, dealers, or live auctions.
I think this only proves that meeting a dealer, going to shows, and networking with fellow collectors is an activity that's priceless. Information is key....