How much magic did king Thranduil and the elves of Mirkwood possess?

Question

We know that they are not as powerful or as wise as the high Elves of the West. In The Hobbit (book) the wood-elves put a spell on Thorin when they capture him.

"Consequently Thorin was angry at their treatment of him, when they took their spell off him and he came to his senses" (from the chapter "Flies and Spiders").

Then the Elvenking talks about the magic of his elven gates or rather the magic on them.

"There is no escape from my magic doors for those who are once brought inside" (from the chapter "Barrels out of Bond").

So, while being lesser Elves than the Noldor, how much power did Thranduil, a Sindarin Elf, and the silvan Elves possess?

Answer 1

Aside from those cited in your question the only definitive statement of the magic of the wood elves is given in the Hobbit chapter Flies and Spiders when discussing the kindreds of the Elves:

Though their magic was strong, even in those days they were wary. They differed from the High Elves of the West, and were more dangerous and less wise. For most of them (together with their scattered relations in the hills and mountains) were descended from the ancient tribes that never went to Faerie in the West. There the Light-elves and the Deep-elves and the Sea-elves went and lived for ages, and grew fairer and wiser and more learned, and invented their magic and their cunning craft, in the making of beautiful and marvellous things, before some came back into the Wide World.

So although they're definitely less powerful than the High Elves, their magic is still said to be "strong". This is not something that Tolkien actually quantifies in any other way however.