The 300RR was designed as a Race Car by Russell Carr, who designed the new Elise and Exige 2.
When the Original designer works on the race car (300RR) adding the wider arches and inlets that was required in the race car the design is more cohesive, it looks more "together".
It's always difficult for another designer to work on an existing design and make it look better as he/she would have different ideas which may or may not work with the original design.
That y IMHO the 300RR looks as awesome as it does.