Sounds like the springs are toast. Not all springs are the same. Cheap no names typically won't last as long as good ones. Take them off and check them. If they are not square or have lost ANY free length, junk 'em. I've come to the point where I see coil springs as consumables like valve springs, slicks and spark plugs. They are usually not replaced as often as they should.

Not to start a crap storm, but shocks have a small window of where the installed length should be. That window moves some depending on the type of suspension (4 link, ladder bar, leafs) and how the car is used (street, drag race only). A heavy spring will only be compressed a small amount to hold the shock at that correct length at ride height, while a lighter spring will need to be compressed more to achieve the same result. A lighter spring will also store more energy to help make the suspension more "lively" IF needed. (Think about a smaller torsion bar on the front to help get the front suspension moving, same effect). Lots of folks see that spring rate choice as a tuning decision that is affected by power levels, suspension type, gear ratios and trans type, tires, desired aggressiveness of the suspension, and many other things. Likewise, some people will run the springs at different compressed lengths from one side to the other depending on how they want to set the car up, distribute weight, etc.