Features, past the minimum required to produce value, make almost no difference whatsoever on reach.
Marketing, sales, and solid communication of delivering value do.
Thought experiment: do you buy MSWord because it has more buttons than Apple Pages?
Or rather is it the de facto standard in your group because of business forces and adoption is driven almost entirely by quorum?
Inside business class apps you can typically achieve more virality if there is overwhelming benefit to people interacting in the same system. Still it's not really feature number or the way you take advantage of mobile APIs but rather by providing an unimpeachable value to the user.
Second thought experiment: facebook makes it harder and harder to share content outside its platform. People still use it. It's actually creating dis-features. But the value of the network outweighs even the (intentionally) bad design and people use it.
So value proposition first. Everything else is details.