It very strongly depends on what kind of product you're developing, and who your target market is. For a Web2.0 social app, skip the salespeople.
For an app that capitalizes on your MS in material sciences and love of python, and targets big manufacturing companies, an experienced sales team is worth quite a lot. Viral won't cut it.
As oppose to a slick ad copy written by (very expensive) professionals.
The gist of it is that if your product isn't cool enough to the target audience that they want to tell all their friends about it, then it's probably not good enough to make serious money.