You WILL NOT need spacers if you get legit aftermarket wheels.. They will most likely limit your selection of wheels though.
Proper aftermarket wheels are made at varying offsets, it's just a matter of finding the right offset. I had a set of Speedy 15" Hyper Fang's (http://www.speedywheels.com.au/images/zoom/hyper-f ang.htm) on my old KE30 Corolla (basically the same car). Didn't have spacers on them.
As a side note, I've currently got some rims off a Silvia on my KE55, the offset wasn't quite enough and the rims were rubbing on the struts, so I swapped them for a set off a XT130 Corona. Obviously the rear look a bit odd, they sit in more, but I'll live with it.