That said, I think there are some things that could be done to improve bitcoin, such as further developing the idea espoused in this article:

http://blog.cryptographyengineering.com/2013/04/zerocoin-making-bitcoin-anonymous.html

The cryptography underlying this technology seems to still be in it's infancy, but when it's ready I think that it would be an excellent addition to bitcoin (no need to start a whole new coin, let's just integrate it into the Bitcoin protocol).