Question posted Feb 2008.
I think JW has solved the issue.
However, it is somewhat a timeless question.
Yes, de-cluttering is important, but not for the reason given.
A knowledgeable REALTOR can see past the clutter, confusion and disorganization. However, seeing such things may suggest to the REALTOR your level of commitment to the process is less than 100%. Helping you sell your home is a team effort. Without both the owner and REALTOR being on the same page, striving for the same outcome, the journey can be distressing.
DE-Clutter to show you ARE planning to move.
When you home is listed, de-cluttering will be essential to get you the best price.