I've done all the M3 suspension parts, aftermarket dampers, springs, custom bearings and so on. Here's my three cents.
1. Upgrade to the M3 front control arms/tension struts. The part # on
www.getbmwparts.com is: PKE9XM3ARMS
These will noticeably improve the road feel through the steering wheel. The M3 suspension components use harder bushings which contrary to popular opinion, don't make the ride harsh (harshness is totally attributed to the damper/spring combo).
2. Upgrade the dampers and springs. Everything else in the suspension save for the tires is of tertiary importance as far as performance goes. The BMW Performance kit is a safe bet. Springs and Koni Yellows/Sports are a midrange choice and TC Kline is a high-end option.
3. Get camber plates; I like the Ground Control ones. These will add to the steering feel too and let you get more camber in the front = more grip through turns. I run 2 deg. which is as far as you can go on the street without excessive tire wear. I would do 1.5 deg. for a street-only car.
Spend money on upgraded dampers and springs before considering a stiffer sway bar. The purpose of a sway bar is to add spring rate in turns by connecting one side of the car to another - a tuning tool. They're pretty much last on my list of things to address upgrading a suspension.
Best of luck.