It is unusual to need to replace the coil springs, unless they are broken. Replacing the springs is not needed and only adds to the expense. What is far more commonly needed when replacing struts is the strut bearing plates which turn with the struts when you turn the steering wheel. Over time these wear out, get rusty, contaminated with dirt and don't operate smoothly and quietly anymore. When replacing the struts, the bearing plates should be checked to see if they need to be replaced while the struts are out of the car, so you don't have to pay the labor twice if they fail in the future.
Lowering springs compromise the ride of the vehicle, meaning it will ride stiffer and provide less comfort. Riding stiffer, this will transmit more of the shock of hitting road irregularities such as potholes, etc., to the struts and the entire suspension, with the end result being parts will wear out faster. $$$ With the vehicle being lower, it is also far more likely to have damage from hitting curbs, high parking lot entrance ways and also bumps in the road, or speed bumps, which can damage the exhaust system and other under-car components.
Advance Auto Parts has high quality Monroe struts for your Corolla on sale at about $100 each and if memory serves me correctly, I think they have a lifetime warranty through Advance. Below is the link. I hope this helps you out.
http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_oespectrum-strut-monroe_15930298-p?navigationPath=L1*14921%7CL2*15010
- Monroe Certified Ride Specialist