No, valvesprings are normally only checked if the head is off for overhaul.

From the difference in deposits the #3 cylinder may have a problem - possibly too lean, which got it into detonation and overheated the valves. As part of the repair you should either have the injectors flow tested or just replace them.

It's often difficult to differentiate between the root cause of the failure consequential damage. It would be unusual for two valvesprings to break simulataneously, but one could break, causing the valve head to break off, then that could jam in the other valve and break the spring.

Overrevving could also be an issue, but I rev my Cosworth Vega to 7000 regularly, and the production springs are good to 9000 with the higher lift racing cams.

Duke