If you haven't already figured it out, you do not need all that many sites to build an effective RSS link wheel. If you do some searches on "link wheels" you will see that some SEO companies offer services to build link wheels with anywhere from a dozen to several hundred websites involved. That many sites probably is not going to hurt your SEO efforts, but at the same time it also could be considered overkill.
I find that an RSS link wheel works just fine with only 5-6 website properties. I think it is more beneficial to create more links to the individual link wheels once you have them up and running.
You can treat the websites in each of the link wheels as targets for other kinds of link building activities. You can bookmark these links and internal pages on a few of the social bookmarking sites, and you can use some of the semi-automated tools for this like Stumbleupon and many bookmark services provide as tool bar buttons. Some that I use occasionally include sharing buttons for Twitter, Facebook, Bing, Diigo, Friendfeed, and Clipmarks.
You really don't need a lot of these kind of links. The important thing is to mix up the type of links, and then just from time to time 'bookmark your bookmarks" using different profiles. There are automated tools available for bookmarking, but this too is an option and not really necessary.