I question the use of the word "upgrade" when talking about lowering springs and shocks/struts. Anytime you go from the original springs and shocks or an oe equivalent you are going to lose a lot of that ride compliance that soaks up those bumps and holes for you. Couple that with the typical choices that go to larger wheel diameter and lower sidewall tires with higher inflation pressures and you have a really crappy ride in my opinion.
To me the stock setup handles better than most stock sedans out there and makes it a really nice comfortable ride for old geezers like myself. I have stock springs with bilstein oe. shocks and stock 15" inch wheel size with stock size tires. My e46 touring has the sport suspension,sport wheels,sport seats package and i can only take it in small doses. In fact i'm trying to decide if i'm going to keep it. If i do i will probably order the rough road package that the south african market shows in the etk which has taller longer travel springs and shocks, I'll also go back to the stock wheels and tire size since roads here in Tucson are so crappy and only getting worse. It will save the oil pan and lower spoiler along with the temp sensor from getting scraped off regularly here.