As an affiliate marketer I'm looking at using RSS AutoResponders to increase my conversions...especially on high ticket items. I think it's a great marketing platform that shows the progression of RSS as an effective marketing tool.
By downloadable application I'm assuming you're referring to a merchants specific feed aggregator a user could download to their desktop and not to regular aggregators such as Feedreader, FeedDemon, NewsGator, etc.
If this is what you're referring to I belive it's a waste of time and money as generic aggregators are perfectly suited to getting your news out.
Please clarify if this is not the premise of your post.