As for why Morgoth didn't destroy the Silmarils, apart from wanting them, I don't think he could have destroyed them if he tried. They were holy jewels and burned him if he touched them, and they can even survive in the molten core of the earth, where one of them finished up. Morgoth couldn't have destroyed them even if he wanted to.
In response to the Noldor, Morgoth did almost succeed in wiping them out, with them only having one major settlement left, the havens at Tol Sirion (I think that is what it was called) and this was then destroyed by the sons of Feanor. If the War of the Wrath didn't occur, the Noldor (and other elves) would've been completely wiped out from Middle Earth in a short period of time.
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His sword was long his lance was keen
His shining helm afar was seen
The countless stars of heavens field
Were mirrored in his silver shield
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