If you download the training simulator it gives some values for the elastic effect on the coef tab. From the simulator it seems rather small. To me it should not be a factor in how you setup your players. For instance handling training can be boosted by outside defense. However, its usually better to train handling as you are training driving (unless the player is extremely short).
Others feel it is more important. However, I tend to accept research.
It may be effective to train IS before ID/RB. But it depends on how you want your player to end up. You may not want too much IS. That sort of thing.