Foamy oil means the spheres have definitely gone. The foam,as I mentioned is nitrogen gas .
A crook valve will only stop the car going up or dropping quickly when the engine is off. They are very basic with nothing much in there to go wrong. If the plastic ends on the link rod are broken,buy a new rod but again,they won't affect the ride.
Your ride feels soft(ish) because the tires are absorbing the worst of the bumps. When working properly the ride is fantastic in a 300. They make the old comodes and Fallcans seem like horse buggys in comparison.
The spheres last about 10 years of average driving ,more on babied cars and less on those used for towing boats etc.
The shocks are actually hydraulic rams and the springs are just there to support the weight. they don't do much else. The spheres are the actual springs,and the oil in the rams is pushed against the diaphragm in the sphere. The nitrogen is compressed and that is what gives the car it's soft ride.
If you are unsure,it's not a hard job to take off the flex hose at the sphere and poke a wire into the sphere and check how far it goes in.