Why would you pay someone for a tweet? They posted it for free. Collecting tweets isn't journalism. Asking the user for more than 140 chars about what they are witnessing along with multiple others would then be closer to journalism. Tweets are just people self identifying who journalists could be interviewing. The interview allows for follow up to the tweet.

If I see tweets in any article other than tweets from the people that the article is about, I will throw that news site in the dust bin. Using tweets as evidence or as anything important tells me that news site is definitely in a death spiral. I think the only place I put up with it is on the local news and even then I'm gritting my teeth.