The realism element of the BRCA rules has been enforced as best as possible in recent years to try and avoid a situation where a touring car shell is a blob and a 1/12th shell is a cheese wedge.
It is thought by many racers that people from outside rc are more likely to get involved with the sport (and in particular on road classes) if the cars they see racing round their local track resemble the full sized versions on the TV. This is understandable, and one of the reasons why so many people follow the full scale world rally championship; they see a ford focus roaring through a forest at 100mph, and then see it again the next day in a car park at work!
However, it has been noted that the modern paint schemes, lighting styles etc... used by many drivers now mean that recognising a model car body shell to be a representation of a real racing car is virtually impossible; Only other racers themselves can regognise different shells on the track if they look very closely.
I think the rules have been relaxed this year for that very reason, although i think measures still need to be made to ensure we don't end up with slot car bodies like russ has pointed out.
Don't get me wrong, I think the speed 12 is a great looking 12th shell, but my favourite is the protoform speed 8, purely because it resembles the real car forward of the 'scoop' better than any of the current shells in my opinion. Having said that, theres no way I'd use it for racing when there are shells available that give better performance!
Just my 2p's (or should I say 2 cents?!) worth.
Mark Stiles - UK BRCA 1/12th scale national competitor