THE COLLE SYSTEM DVD by Nigel Davies is a good source for the discussion of an early c2-c4. Many times he points out how a Black set-up that works well against the standard Colle-Z is mis-aligned against the hanging pawns structure that results from White's c2-c4.

I used to hate the idea of c2-c4 because it meant I couldn't try for a Colle-Z type bind with the N on e5 supported by pawns on d4 and f4. Then I bought a book on hanging pawns, learned their strengths and weaknesses and now play c2-c4 with confidence.

I honestly believe the Colle Zuckertort/Yusupov is the best amateur opening out there. It's easy to learn and has the soundness and power of a main line GM opening.