I wouldn't be so quick to cash in older EE bonds. Older EE bonds generally had better terms than the current ones, and some much so.
Revently, EE bonds went to a fixed income format. These bonds are not a good deal in the current interest rate environment, and so if you bought EE bonds after April 2005, I think those are the ones to sell.
However, if your EE purchase was before April 2005, I suggest to go to the Treasury Direct website and look up the terms of those older bonds. Some of those bonds have floors of 4% or even 6%. Those are good rates in today's environment, regardless of how well the I-bonds look.
I would purchase I-bonds with new money or money proceeds from the sale of EE bonds purchased after April 2005. I'd be inclined to keep the rest of the EE bonds until you want to spend the money, or until they reach final maturity.
Steve