Well, I'm using DNNv04.05.05 with the default announcements module on a page, which I've set to syndicate. It does show the RSS icon whether I'm logged in or not. Not sure why your's isn't.
As far as the auto-detect of syndication for IE7:
Using the ADMIN sign-on, go to the page where your syndicated content appears. In the ADMIN toolbar, click settings. Expand the Advanced Settings area, and place the HTML code snippet in the Page Header Tags text box. I use this HTML code:
<link rel="alternate" type="application/rss+xml" title="iwonder's experimental site newsfeeds" href=http://localhost/dnnv040505/RSS.aspx />
Of coursse, substitute your URL, but don't forget to include the last bit RSS.aspx. Now, sometimes the syndicated content may not show up, but that's due to caching, which you can get around by using the HOST account and using the Search Admin option, and clicking Re-Index Content. Other areas to investigate are the site's Schedule options, specifically the DotNetNuke.Services.Search.SearchEngineScheduler, DOTNETNUKE options. Play around to get more frequent refreshes of the search content, because that's what builds the internal RSS feeds syndicated content.
Cheers