Over time and load cycling ALL springs sag-change shape, it is a matter of degree.
The absolute head-ache of serious racer folks is inconsistent springs. Good quality springs have their actual spring rate marked on the end. With this specification, the overall height of the spring is measured to x.xxx" , spring rate measured to fractions of a pound -vs- loaded height then the spring is serial number with the measured specifications logged. After a few races and chassis test, when the springs come out, they are checked for variations from original new.
In the case of stock springs on the exxe or most ANY street driven car, slight variations in spring rate is not really noticeable at all due to condition of the dampers, rubber bushings, road surface, expectations and sensitivity to chassis condition and all that. Fact is, street driven cars are not competing for the last 0.0000x second of lap time for field position.
New springs and dampers are a good thing. These are known wear items that are extremely neglected yet paramount to chassis performance and dynamics. The neglect comes from the idea and belief, "if it's not busted, why fix or do anything about it."
IMO, $700 for a set of four springs and dampers is NOT expensive. There are car folks who drop FAR more than that on two tires for their "Performance ride".. and those tires last maybe one track day if even that.
Bernice
what those of us who enjoy the X 1/9 in its mostly stock configuration would really like to know from those who are swapping springs around and such: It is said that after several decades the stock springs -which cannot be purchase anywhere except in used and presumably sagged form- are lower than the Vicks short springs. Can anyone speak to that theory? I sure would like new springs, but I just don't want to go any lower than what I have (old stock) now.