My honorable mentions would have to the spinning coaster clones made by Maurer and Gerstlauer. They're fine for for what they are, but there is very little difference between the spinning coaster clones.
Busch Gardens
Williamsburg:
* Not letting B&M build Drachen Fire
* Melting down Drachen Fire for parts to build Griffon
* Removing Big Bad Wolf for Verbolten
Tampa:
* Letting one side of Gwazi rot
* I can't really think of two more "mistakes" for BGT!
Although, I never rode any of these coasters, but I think that cloned coasters are underrated because they are mass produced and can be found at many parks world, more specifically the "Boomerang" models.