Everyone has a different experience of all these attempts to get recognition. So much depends on the genre.
I looked on youtube for a clip from the movie Independence Day where Julius says to his son, David, something like "These people are vultures. They take and then they go." I couldn't find it.
The promo at Smashwords was just starting to become uncomfortable for me the last day. My bones weren't picked clean, though.
Dream Horse and Murder Is Exhausting are about halfway through their giveaways at GoodReads and so far I'm pleased. You must give away a physical book, not an ebook. You can give away as many as you like and it seems that 4 weeks is about the longest any of the giveaways run. That feels too long for 1 book to me. A moderate number of people seem interested and have put the books on their lists. Will there be any sales? Who knows but at least it was some exposure. (I would like to know why 9 people have Last Junior Year on their TBR list when the thing has been out of print for decades. Where are they getting this book and why are they bothering? Are you telling me there is nothing current like it? And no, I'm not going to republish it. But I looked at the cover today and I think I did a good job on it. Yes, the first two books I published with Atheneum used photos I took for the cover art. Cool, huh?)
Is it worth it to format your book for CreateSpace and spend the $10 (approx.) to get a proof copy to give away for the exposure alone? I think so. After all, that $10 also gets you (although it could be free if you skip the proof) a paperback forever on Amazon that gives you more shelf space to take up, more opportunities to be found.
If you love Kindle Select and have good to excellent results you probably won't want to bother with GoodReads. If you haven't gotten the results you wanted with the freebies at Amazon, maybe you should try 1 book giveaway at GoodReads.