Good Feedback, bullcityrob.
It does take some time to go through the emails, it is the perfect job to outsource to an assistant, VA, your teen...
And yes it definitely isn't worthwhile to respond to smaller outlets that want full content upfront, unless you have a body of work you know you can easily repurpose and the outlet is big enough to make it worth it. If you have more time than marketing budget, it is a useful tool :)
It's also useful just to see who is out there and what content they are looking for. Useful for market research. If there is a topic that is coming up a lot, it is a pretty good indicator that it is a popular topic that if you do create your own content on, people will be interested in it.