I like the clean look of the 04 better than the scoops and rear diffuser on the 05 -- but the higher output of the LS2, bigger brakes, revised TC and split exhaust tips are definitely worth looking at.
Just depends on what your priorities are in life. Would you rather have $8K in the bank -- or an extra 50 hp that you'll use every once in a while? Of course, you could get the 04 and install a SuperChip -- and close that 50hp gap quite nicely.
BTW, the 04 does have true dual exhausts. The pipes are separate. They just run parallel to each other and exit in back of the driver's side. The Aussies had to run it around the gas tank in their Monaro.