Congratulations on your BookBub! You know, SW is not advertised by BookBub. You can advertise there from other promos and you might land a few crossover sales, but I wouldn't focus on Smashwords. If anything, I'd add advertising to Amazon (of course), GooglePlay, Apple, and/or Kobo.
Whenever I run an international BB promo, I run domestic sale promos at the same time to take advantage of the intl BB sale. And this does garner more US sales than without the BB, I think (outside of Smashwords).
I've stopped focusing on Smashwords. I used to advertise there and I'd make some sales, but it wasn't worth the cost. If you sell erotica, I hear it's different. Erotica sells very well at Smashwords. Also, 2x/yr, smashwords runs an inner store sale that sometimes gives me a sale or two.
edit} What I'm trying to say is, ask yourself if it's worth it to focus marketing there and not elsewhere. If you sell really well there, then go for it, of course.