I think you can pursue those two goals, its just the copy that needs a little work. A user coming to your page is going to know which bucket they fit into (pro or newbie). If a pro user comes and sees "learn how to sign up for Twitter" then they might leave before fully investigating because they think the site is obviously not for them. I would take out that line for sure.

An idea might be to segment your users up front. So the front page would say something like "Our service can help anyone interested in social media, from small business just learning how to use social media effectively to power users looking to gauge influence, find optimal posting times and understanding customized analytics."

Then the newbies get sent in one direction with a button "I'm new to this, tell me more about social media"

and the pro users get sent in another "I'm pro user, tell me more about how you can help me"