The 'silver stuff' is the plant weight and is sometimes made of lead, so I always remove it. I don't want lead in my fishtank, especially as I have invertibrates which are very sensitive to metals in the water.
The foam can be removed but only if it can be done without damaging the plant's roots if it it has some.
However, I usually leave the foam on as it protects the roots from snails and herbivorous fish. The plant will still be able to spread and push it's way out of the foam. (ever seen grass pushing through a concrete path?)