The best thing you can possibly do for getting more unique content is to encourage user-generated content which is typically in the form of reviews, but can be anything (photos, video reviews, FAQ's, etc).
Product descriptions are inherently and necessarily non-unique. I really believe that simply spinning phrases or rewriting a paragraph here and there is a low value activity. A much more sustainable activity is to pick a handful of interesting, current, high margin products and create the absolute best page about them on the web. A personal story, a groupon-style humorous reference, some unique research... whatever, and just dominate that product with content. You'll rank for that and also probably earn some love from customers for being so cool. Keep doing that one by one and carve out a niche. I bet if you do that 10 times really well you'll get a much better ROI for your time and/or cash than 10,000 pages of slightly varied copy.
Unique content only goes so far. A strong domain with piflered copy will outrank others with the same content all day long. They sometimes even beat sites with totally unique content. As unfair as this is, building domain authority takes of time and investment, and is rewarded with traffic for having trusted content.
Finally, my dablings in the dark side have taught me that Google is getting much smarter about spun content, aka content that is thinly unique. 30-40% unique is definitely not unique enough. Varying synonyms is not enough. Significantly unique content varies in theme, length, and style - all of which are algorithmically detectible. Hope that helps.
