Yes, a user without an account can create unlimited feeds, but those feeds self-update much slowly (as compared to feeds for a user with an account), and secondly, a user without an account cannot manage all their feeds in one place (i.e. to edit the feeds later, to check stats, or to create streams etc).
But I still think that the number of feeds for a free user is ridiculously low.
I think that you should double it even if it means reducing the refresh rate for all feeds (or maybe having a "normal" refresh rate for the ten first feeds and a "lower" refresh rate for the other ones)
Edit: And you don't have to tell the users about it.
Give our startup a try, to create a custom RSS feed: Feedity - http://feedity.com