As Don said, some coin collectors will keep examples of fakes for reference. I have a couple, and they're interesting. Fakes done in the period can be collectable.
It's the same with stamps. Some collectors and I believe all of the expertising organizations have some as a reference collection. Many of the most dangerous fakes can be traced to the original forger, and in a few instances a philatelic organization has exposed the forger but purchased their entire stock and forging equipment. In the case of the most skilled forgers at least one had the remaining forgeries put into books and sold. And some of the forgeries are worth more than the originals.
Sperati was among the most amazing technically. And some of his sell for a very good price.
http://www.glenstephens.com/sperati.html
And a page with a few more of the better ones in a specific specialty.
http://www.jlkstamps.com/fakes/fakecsa.htm
There are a few baseball card fakes I'd consider collectible. The rose rookie fakes are available and I'd like to get one someday. Even one of he ones marked as fake. Plus most any that were produced in a small time period in the early 90's. Those all required a bit of technical ability since they were printed on a press just like the actual cards. The newer generation of stuff printed on a printer from a scan aren't all that interesting. I do have one, and while it was a maybe in a blurry Ebay scan it's obviously fake seen up close.
I also have a fake E121 I got in 1978. Strange card, fake, trimmed, and a ton of work for the $2 it cost me.
Reprints are a different thing. I suppose I'd go for a few of them, I wouldn't mind a T201 set that I could fold and play with, reprints would be perfect. Maybe a reprint of one of the game sets, so I could play it. Other than that I enjoy a single low grade original more than a fistful of reprints.
Steve B