Spring Social Twitter only recently started supporting Twitter's streaming API. But that's for Java and your question is about SpringSocial.NET. I doubt that SpringSocial.NET has support for this yet. But I'll ping Bruno (the SpringSocial.NET project lead) and see if he can chime in here.
Until SpringSocial.NET supports Twitter's streaming API, your options are to continue polling (which is non-ideal due to rate limiting concerns) or to implement streaming support on your own. I'm sure Bruno wouldn't mind a pull-request to add streaming support to his project. :)
To be clear, SpringSocial.NET is not the same project as Spring Social and the two projects are only loosely related (in that I know who to email if there's ever a question about SpringSocial.NET).