It is not rare. But it is not common.
Opel GTC was created in 2007.
GTC Wireless was created in 1997.
A number of models that have been used recently in races includes the F10, the F60, and the F430 GTC. A list of Ferarris that have been used in professional races can be found on Ferrari's website.
That depends on what you call a genuine four seater. Ferrari has had a long line of 2+2 seats meaning that there is actually 4 seats however they shoudn't be confused with the true 4 seater coupes made by BMW, Mercedes, Masserati etc. Some of Ferrari's 4 seaters include 250GT, 330GT, 365GT, GTC/4, GT4, 412, 456 and 612. That's eight on my count
The 2012 Bentley Continental-GTC has 48 valves.
The 2010 Bentley Continental-GTC has a W12 engine.
The 2009 Bentley Continental-GTC has a W12 engine.
The 2008 Bentley Continental-GTC has 48 valves.
The 2007 Bentley Continental-GTC has 48 valves.
The 2013 Bentley Continental-GTC has a V8 engine.
The 2007 Bentley Continental-GTC has a W12 engine.
The 2014 Bentley Continental-GTC has a V8 engine.