+1 impreza. I would go for a year or two old used and under 30K miles. But I prefer the new 2.5 engine to the new 2.0 personally. You will be spending 15k. I drive an 08 5-door and love it. But get the manual. The automatic robs it of so much performance. I see +3 mpg, and I am a lot quicker light to light against my friend. It is a blast to drive in the snow...
And ANY after market stereo will be better than your stock system. really, ANY. and you would pay 1000 for the factory stereo upgrade when you could be 6-700 for one that is extremely superior. If you are mechanically minded at all, do some internet research and it could take you 4-5 hours to install a full system. Or ask around and someone will know of a good place or person to get it in.