I tried a showcase when I first opened, although I read a lot of negative threads about them. I think as a seller you need to try things for yourself and see what works for you. It didn't bring in any sales for me, but did increase views and got some hearts and shop favorites -which is always good when you are starting out. I don't think I would try it again. I've seen results with search ads and would probably invest in that instead.
Good luck! Also, the spot in the showcase changes every couple hours, so at some point you will be in top four just so you know. I would also recommend keeping an eye on your stats -if the featured item isn't getting the views you want, try another one and see what is most popular.
On a side note- LOVE this dress!
http://www.etsy.com/listing/92580356/