I can't really say much for paying to market, as I don't do that, but as far as outside marketing, I personally find FB, Twitter, and Pinterest to be the online sources I use. I also play team games for my new items to get them seen.
A good strategy is to pick a theme for your store. You have a bunch of items that don't go together at all. I can't speak for all vintage stores, but logically, I can't see how it would make business sense to not have a theme. You have glass dishes, and figurines, jewelry and art, shoes... it is all over the place. If you could narrow it down to a simple theme, maybe do victorian, or edwardian, or mid century... then you would find your buyers. As it is, I had a hard time navigating your items because they are a bunch of different styles. If a store doesn't hook me at first glance, then I am not really interested. I would also rearrange your store so that your items are mixed better. Your first page only has glass I believe... maybe a brooch. As for your featured items, always change them up so that there is a variety. Also, try not to put super expensive items in your featured items because someone will take one look at your general pricing and not bother to look at your less expensive items. Having 5 stars and a bunch of sales is good, but only serious buyers look for that. If you want to attract someone into being a serious buyer, you should change up the look of your store. Settle on a picture theme as well and style your images accordingly. You want everything to be seen by someone and have them think, 'yes, that is my style...and yes, that is too...' you don't want just one time buyers after all. In order to advertise my items, I try to post an item every few days when I can. This keeps my items current on the news feed of my followers. They know who I am, and they want to see that stuff. With every new item, I also share it with Twitter, FB, and Pinterest. This way, all of my followers on those sites will also see I have new things. I then play thread games with that item as well so that Etsy has a chance to see it. It is a lot of work, but I'm not sinking my money into advertisements that just put my items at the top of a search bar. In all reality though, playing games is what gets stores noticed. I can't say why your sales suddenly dropped. I don't know what in your store changed if anything. My only idea on the matter is that it could be because the holidays are here and people are paying etsy more money than you to feature their items above yours. But, that could be wrong. I have no idea. So anyway, that is my basic advice. Advertise by playing games, not spending money... and theme up your store.