This Elvish cloak is a niche card and has lots against it on the outlook. There are other, better attachments that boost raw defence, it's limited to Noldor and Silvan, limit 1 and it requires to be played against quests that have forests to even gain the +2 defence. However, there are 2 aspects to this card that I believe make it stand out and warrent consideration in deckbuilding.

The first is that is it only 1of 2 attachment cards in the Lore sphere that provides a raw defence boost, the other being Protector of Lórien. In multisphere decks, it may be worth considering your defence boosts to come from Lore if you already have too many cards in the other spheres to help smooth the resources. Cloak may also gain the edge over Protector if discarding cards to fuel Protector is an issue and you would rather the static +1.

The second advantage is that Cloak is a raw defence boost that is not limited to Heros, it can be played on Noldor and Silvan Allies. This flexibility in the right decks, specifically decks that are wanting to use allies are thier main line of defence, makes Cloak a more viable choice. The best allies that come to mind for Cloak are Guardian of Rivendell and Greenwood Defender. Noldor decks in particular that utilise Círdan the Shipwright and Narya can turn two Guardian of Rivendell allies into brutal defence and killing machines whilst making them a bit more durable against those higher attack enemies.

Cloak is by no means a card that has broad applications, nor will it ever be anything but a niche defence attachment in certain decks, but it has it value and will help keep some of your defenders alive.

Unsure on this card. It doesn't even seem to find a way into my Silvan decks when I play Thranduil and have resources. Perhaps Elrond is a better target?

1 resource for 1 defense can be okay, Dunedain warning is used all the time, but in a more rich sphere and not limited to one per character. I don't even really keep this on my sideboard since I'm not sure how many scenarios actually have forest locations. And even then you can't rely on it too heavily, what if you just draw enemies and now you have no forest location to travel to and extra attacks to defend with just 1 extra .

Sadly, I think staying true to the theme of the card makes it too weak to see much play, at least for me. It's a shame too, it's a pretty card that at least attempts to fill a distinct weakness in Silvan decks.