95%+ of IMers that find the need to spin their content would be doing so for the soul purpose of building backlinks.
If this is the case, there is absolutely no benefit in spinning an article. Common sense makes it easy to realize Google counts the backlinks from each and every article it indexes no matter if its duplicate or not. All the best content websites on the internet have been duplicated hundreds or even thousands of times by other webmasters who thought the content was good enough to republish and link to, from their own websites.
I believe that its a myth that Google count and index less articles per bulk article submission than if the same article would have been spun. If Google was to do this, there would then be large portions of the internet road map that's known as the Google Index. Googles rankings would not accurately represent what is truly the most relevant and popular websites for each search term.
The reason it appears that less dupe articles are indexed than the spun versions because Google filter out the dupe content from the visual results to give the searcher more variety in their search results. Does not mean the articles haven't been crawled, indexed and backlinks counted. Webmaster tools is now proving my point more than ever with their highly accurate backlink counts.
My point is, spinning articles that are still high quality takes an enormous amount of time compared to a stock submission, sometimes 4 or 5 times as long. That means you could possibly submit 4 or 5 times the amount of stock articles than you would high quality spun articles resulting in 4 - 5 times as many backlinks in the long run. Efficiency is vital in becoming an internet marketing success. So try not to waste your time on something that may only have a little benefit when it takes you 5 times as long to accomplish.