I'd look very carefully in NOT cashing SB into 529. Your SB are probably I-Bonds, and if you believe some people on inflation, then the bonds are a good hedge vs regular bonds, stock, or RE. Besides EE Bonds are unrestricted on use.
Google: Savings Bond Wizard (Dept of Treas), Savings Bonds Books (a book on savings bonds and written by advisor similar to Hurley).
Our EE's saved our butts. Our EE's were prior 1989 and guaranteed 4% after the variable period. Our loans were 3.5%. College price increases were 5%. It was the interest on the Bonds that paid the interest& principal on the student loans and kept our credit scores high until which time the stock market recovered 2005-07. The Bonds were in son's name so he paid the interest taxes, 15% marginal tax rate. I also had DS roll some EE's to 529 stock funds because by 2005, EE's were yielding 4% vs stock funds 10%+ and no commission fee in 529's.
I had son cash bonds in his senior year, 2005-06, when we were able to lock in the student loans on a fixed rate, and to pay his senior year expenses.