I don't think RSS helps rankings directly. The only site I added an RSS feed to (which gets updated very regularly) didn't see any appreciable increase in traffic. If you have good content that making that content more easily available (e.g., through RSS) could mean more readers which could mean more backlinks if they like your content, but I wouldn't expect adding RSS in and of itself to increase rankings.
My general advice is always that if you want good rankings, make your site deserve the rankings, and the rankings will follow. If your site offers info, make it awesome info and easily accessible. If it's a store, be the best at something among all your competitors (price, quality, service, easy of ordering -- pick one or more).
Indirectly it could help seo rank in a couple scenarios providing links are contained within the feed back to your site...
1. Some sites take your RSS feed data and repost it on their own site (XML to HTML), which if the URLS pointing to your site in the feed are left intact, will count as inbound links.
2. Additionally, if people subscribe to your feed, read the posts, visit the links to your site and add that link to their favorite social sites or own site, it could ultimately translate into more SEO juice.