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.