It isn't neccesarily obvious, but you can look where the body bushing supports the sway bars and see some wear. But if you take off the old bushing and compare it a new one, it becomes very obvious.
To illustrate how I feel about it, when I bought our wagon ('95 with 55k miles) I immediately change the front and rear sway bar bushings. Made a noticeable difference. Less sway f&r and more resistent to cross winds.
For a DIY job, replacing the front and rear sway bar bushings is quite easy. I would replace these if I just got a 500E with 60k miles. As a matter of fact, I am looking forward to doing that some day! I do replace these bushings with EVERY Benz I get. It always makes a difference.
Remember the fronts take four bushings (2 for each at the lower control arms and 2 for the body links) the rears only take two.
Sounds like you are attuned to your car. It is often said that what you do to one end of your car influences how the other feels. Thus if the back "feels" more sway, it could be worn front sway bar bushings.
Let us know,
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)