Feed subscribers often referred to value our advertisement slots. But, it is not the main factor in determining the value. There are other vital points like traffic, pagerank, pageviews, etc that plays core role.
I’m sure you have heard about this from John Chow about tricks to increase your feedburner count numbers. This is dirty way to increase your feedburner counts. I have tried, but not his way. I tried with traditional email subscription way. This is the easiest way to get higher feedburner followers count.
1. Create new email address from any free email network like yahoo, gmail, hotmail, etc.
2. Subscribe at your blog feedburner with your newly created email.
3. Verify it from your email address.
4. Repeat it with any number of email counts you want.
In my case, I chose 15 email addresses as a trial and it is counted in feedcount. This really works. Other than that, you can exchange rss at blogcatalog group discussion. But, frankly, exchanging rss, subscribe using own emails, etc will not be helping in long run. Good contents will help.