It seems like the Subaru's of the same age go for a lot more money. Maybe due to Saab no longer selling cars & Subaru's seem to keep their value better than other cars due to the loyal following.   
On autotrader right now.   
05-06 Subaru WRX, manual, anywhere in the country.  34 cars. 
Highest Price:$18,991 
Lowest Price:$8,500 
Average Price:$14,685   
05-06 Saab 9-2x Aero (turbo=same as WRX), manual, anywhere in the country.  6 cars.   
Highest Price:$12,995 
Lowest Price:$9,250 
Average Price:$10,910   
One thing to note is that even though I searched for 05-06, there were no 06 Saab's since there was such a low amount made and I'm sure they are the most sought after variation (due to 2.5L engine).   
Searching for WRX 05 only.  15 cars 
Highest Price:$17,995 
Lowest Price:$8,995 
Average Price:$13,606