Ex Scooby WRX owner here
After owning a 2002 WRX with 280 bhp for 4 years and now owning a ZS 120, I can honestly say that the ZS has surprised me in regards to handling. MGR did a great job of the suspension (if a little too hard on certain roads), the WRX is a little softer and slightly more forgiving I think and not at all track orientated, whereas the MG seems it to me, (but the classic Imprezas are more raw and lighter than the "newage" versions)
Most Impreza owners dont know how to drive them properly, so at the end of the day its down to the driver and track, but the Impreza could be a bit bulky against the ZS on some tracks.
Even though ive never driven a 180 but have driven a few other V6's, im sorry to say with equally capable drivers in the 180 and Impreza, the Impreza would win in cornering, acceleration from standstill and corner entry and exit speeds, putting the 2 head to head isnt really an equal "battle" (Touge mode on).
The ZS is a cheap and very cheerful car and im happy ive got one, even though I do miss the Scooby.
P.S. Dont race on the road, thats what tracks are for!