I share your concerns. I've been deleting non-answers on all the questions — most of which have been flagged — but Al has undeleted some. I haven't heard from him yet but I would assume he's trying to offer the benefit of the doubt and give everyone a chance at the contest.
I totally understand that point of view, but I am really uncomfortable with flooding you and the other OPs with crap. Not to mention that everyone who sees these questions (a significant number due to the contest) will see the crap and either follow suit or think this site is full of crap. One OP has withdrawn his questionOne OP has withdrawn his question. There are a couple others where the OP is clearly not going to come back and the issue is pretty localized, so the new answers are extra-useless.
SE isn't built for contests and promotions, and it shows. kindle-fire-contest is a "meta tag", and meta tags are thoroughly reviled and discouraged throughout the network. I don't think using one so visibly is a good idea, even though it attracts much more participation than a meta post does. (Gaming has had this low-participating problem with their grants.)
Nor is repeatedly abusing the system message function every time we have a contest a good idea. Android has a lot of hit-and-run users already, and I'd argue that these contests don't do anything to change that behavior without a rep/activity requirement as you mention. And we certainly don't want to drive away users with annoyances.
One option is to protect all the questions involved, but that cuts out involvement without necessarily cutting out all the noise. (Some are being auto-protected by Community, though, so should we un-protect those repeatedly? Ugh.) The other problem is that we can't really change the contest now that it's started without some trouble. Personally I'd lean towards that anyways, if not terminating it, given the trouble we're already having.