Ok, I think I'm finally getting it; Replace every flexible suspension part
 

85k miles. All four front control arms recently replaced. All four shocks recently replaced (Non-sport, OEM). Cornering body roll is 90%-ish back to original stock. Love to get it all back, plus maybe go to 120% of stock, but not 'go too far' and ruin the ride qual.

Was thinking about thicker anti-sway bars. JCL explained about increasing understeer if just the front is done. I was settled on upgrading just the rear bar, either OEM sport ver, or Eibach (even stiffer). But... was surfing the ECS site (has wonderful parts pictures!), and now I think I get it; If I want my 'at least stock ride' back, basically, every rubber suspension part on my car probably needs to be replaced. Even though my mechanic is saying, "Yeah, the other remaining parts look fine. No excess play. Don't replace".

The pics really helped me to get it. The front actually has two anti-sway bars... that's four rubber bushings to slowly wear out.

Why the new post? I'm now wondering if its not just an "Upgrade rear sway bar.. that's all there is left" question. I realize you can't diagnose my car over the net. Just curious on feedback to this point as well; At 85k miles, and in your travels on the net and personal experience, do I need to just go ahead and replace all the remaining parts that have rubber connections involved.. FIRST.. and then start my ride analysis / eval over again on whether to upgrade the rear sway thickness?

This would be ignoring my mechanic's advice, but then again, as a general statement, I think most techs are primarily only interested in maintaining basic drivability and safety, and are not performance oriented.

Here's a funny point for ya: A buddy at work, who has an Acura, was totally shocked that a BMW 'required' suspension parts replacement at only 85k, and that Honda / Acura would consider their parts to 'last the duration of the car's use'' (iow, hundreds of thousands of miles). I teased him that; 'Uhh.. dude.. trust me, your car's bushings aren't made from unobtanium. They're made from the same materials that BMW uses, and, your bushings are gone.. you've just adapted yourself to the loss in performance.. haha..".

Front Anti-Sway Bar With built in rubber links:
BMW E53 X5 M54 3.0l > Suspension > Sway Bar > ES#51108 Front Stabilizer Line - Driver (Left) - 31356750703

Rear Sway Bar link
BMW E53 X5 M54 3.0l > Suspension > Sway Bar > ES#59115 Sway Bar Link - Priced Each - 33551096735

Tell me about it. I just replaced entire front end suspension (ball joints, tie rods, control arms, etc.) at 130k and went with poly control arm bushings, Bilstein HDs, and Eibach springs and sway bars. Should be more than 120% when I get it back this week.

For BMW drivers, the slack caused by work bushings can be felt by a deterioration of handling, that's why we're more sensitive to bushings.

I agree, any other car would need new bushings as well. Non euro owners tend to just ignore those parts because the cars don't handle as well to begin with.