I don't think Bruce (who no longer visits here) was implying there was a problem, rather, that it would be beneficial to eliminate heat build-up and any potential related problems. That would be true for any car.
I'm not aware of any problems with the XLR, but it's not a particularly well-ventilated engine compartment. The grille is solid, and it's basically a bottom-breather with no side cove heat exits like the vettes. Even the new side grille on the 2009 is reportedly not functional. Presumably, if there were a problem, it could have been.
Corvette-wise, some owners of C2's, particularly the big blocks, do sometimes leave the hoods open. I'm not sure it's much of an issue with newer models, although the first-gen ZR1's and the Z06's do get hot. Supercharged cars like some of the Mustangs or XLR-V's would probably benefit, too.
I doubt that it's necessary, and it can't really hurt, but there's always the possibility of unintended collateral damage anytime you do anything with a car. IMO, YMMV, FWIW, etc.
