Maybe not worried, but I'm sure the R8 caught their attention. So far most of the teams fielding Ferrari's and Audi's are new to the grid, not converters from other cars. I think the BMW is the first direct threat to their business of the "European invasion". Best case scenario in my opinion would be the Turner-Riley M3's race alongside BMW teams. I'd love a mixed field like that.
You're right in that Riley still has a pretty strong hold on the segment, but the Pratt & Miller Vettes are certainly one of the first credible chassis threats they've seen in awhile. I'd like to know how much involvement Rileytech had in helping P&M/GM put that program together. I'd love to see Lola or another chassis maker step up to at least put three marques on the grid. I'd also like to see another engine manufacturer return because this Chevy/Ford business with the Ganassi BMW's is getting rather stale. Last year the Flying Lizard Porsche DP was very strong with it's flat 6 and I'm surprised no one else has taken advantage of the smaller displacement=more gears formula that the rules allow.
On that note and in relation to your Mazda comment, how much longer will the RX-8 be allowed to last? Grand Am seems pretty tidy in not letting older cars stick around too long. Since Mazda doesn't seem to have any RX-8 successor that's right around the corner, what if they got it's Rotary approved for DP use? There's some headlines right there!