Well, True Blue does encompass quite a few Mustangs including V6s, GT, Bullitts, Cobras and Saleens. I'm not exactly sure what exactly determines why Yellow and True Blue gets forums all to themselves, but there is a decent amount of traffic in both.
I think the Pace Cars should certainly have recognition, but the numbers in existance probably wouldn't justify having a forum all to itself since there has only been 3 years so far of Indy Mustang pace cars with only a fairly small amount produced.