If you push ebay, they will admit that the various forms of "Pay Per Click" advertising (including Promoted Listings External, which is currently in Beta) are really designed for sellers who are selling multi quantity items, usually new.
While I have heard of a few single quantity sellers say they've made PPC work for them, I would generally say no, unless you are prepared to spend a fair bit of money and energy trying to come up with a strategy that works for you. (Those I've heard who have had some success were single quantity sellers selling in a niche....so I'd say it might be workable for someone who sells only high end jewelry, for example, but for a seller like me, selling a wide variety of single quantity used and vintage.....Nope.
On the other hand, you might benefit from Promoted Listings Standard, which charges a fee only if the item sells. Many of your items probably already show up pretty well in search itself (if someone is actively searching for it) so higher placement in search isn't that important. However, PLS also places your items on the listing pages of competitors, and a host of other places...the value here is someone might not be looking for your exact item, but when they see it on a page like that, it's like seeing candy at the checkout counter....they didn't come to the store to buy candy, but hey, there it is....
So I'd at least consider looking into PLS, but I'd probably forget about the rest.
