Should you buy content for your presentation?
I don't think so. It seems to me to be only a slight step up from the content wizards that PowerPoint contains. These wizards create such poor presentations that they are laughable. In fact, one of the most widely viewed presentations is The Gettysburg Address re-created in one of the content wizards. This is regularly used an an example of why PowerPoint itself is bad (it's not the tool but the user of the tool - but that's another issue altogether).
Instead of thinking that you can buy some standard content, put together a proper presentation structure to guide your message and your visuals. Audiences today will not put up with a presentation that is generic. You need to customize it. And that's only possible when you create the content that the audience needs to hear. That's why the first two chapters of "Guide to PowerPoint" don't even deal with slides. They deal with developing a clear structure so that when you get to creating slides, you understand how visuals fit in to your message. If you haven't got the book yet, get it at http://www.ThinkOutsideTheSlide.com/guidetoppt.htm .