Considering the level of talent already in GTAL, i don't think we need a guest team "to show us how it's done".
How many teams throughout the season are going to sit on the sidelines and say, "Man if it wasn't for the guest team, we'd be racing"?
Giving one more team the opportunity to race could generate more interest....
What if one team, outside the top 10 in points, were allowed to invite a guest driver? Said driver would have to follow the percentage rules, but could boost one team's performance, moral, interest in competing, and maybe even confidence.
I'm sure NDR could figure out an interesting way on how to choose which team would be picked for each round.
My $.02