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This is a great question that many clients have asked me on several occasions. I really do not like any of the choices you have listed. You still risk duplicate content with option 1 as the teaser will still be mostly word for word then a link. If your content is that good they should produce their own content based on the subject and link to yours. This way they are producing fresh content that gives authority to your content.

I would perform an 80/20 analysis and see if these pages are driving any traffic to your website. If they aren't performing well, I would delete them and redirect them to similar pages or back to the homepage. I agree with Bernadette about checking Open Site Explorer. You want to makes sure you are not going to be giving up any valuable backlinks that these pages might have generated.