I'll volunteer some more possibilities:
The struts/springs degrade over time. Even installing new stock replacements can be like night and day if the old struts are worn out.
Tires can also make a night and day difference. After a couple years tires lose a lot of their stickiness, even if they still have decent tread. The best suspension in the world wouldn't matter a whit if the tires were crap.
You put some weight on? Could be slowing the car down too![]()