Theres local tracks who offer Jr Predator classes all over. IMO i dont see a cheaper spec class as smart, sounds more like participation trophy class, not a class you have to work as hard for to improve.
Red, Green, Purple, Blue, plate classes i guess you can kind of say is spec classes all of their own.
Time constraints are sometimes the culprit why tracks combine engines . If a track has a curfew , it makes it hard to run 30 classes in an evening race track . I don't run mine together , but sometimes you may only have a couple per class , so running them together is more logical . I have ran them together before , and scored them separately .