Thank you for your responses. Paul, I agree with much of what you say, but it seems you just don't believe in the value of giveaways. In that case, we can agree to disagree as I have seen them work tremendously well firsthand.
I may not have been clear, which I apologize for. But I am not trying to add subscribers to add subscribers. Nor am I planning to offer a giveaway to the general public. Rather, I am planning a more targeted approach to adding relevant subscribers who are likely to have an interest in the subject matter (inventing and/or travel/kickstarter).
While unncessarily condescending & confrontational, I do agree with some of your more general points and appreciate the time you took to answer. As most online marketers know, giveaways are a tried and true method of marketing. Of course there will always be people who will come just for the giveaway and then not engage, but that is part of any marketing. There will always be "waste" involved in advertising/marketing.
I was asking about the value proposition of the two prize options. As with app and online gaming companies who offer free gaming & get millions of users, it is the 10% of loyal users who pay for a heartier experience that create any revenues at all. Using a giveaway to get relevant users/readers has elements of that as well.
Again, using a giveaway to gain a larger audience among a specific target market who might be interested in the subject matter is a relevant strategy...particularly to reach people who might not otherwise ever hear of you.
All that said, your points are noted and considered. Thank you again for taking the time.