Earlier quoted context omitted.
Marco explicitly asks you not to use the send to Kindle feature 'to automate delivery of bulk content, such as entire feeds.' See http://www.instapaper.com/user/kindle
That just takes me to the Instapaper homepage.
Want delivery of full RSS feeds?
Please do not use this feature to automate delivery of bulk content, such as entire feeds.
If you'd like to do that, try Kindlefeeder, a service designed for (and much better for) that purpose.