We do a new Security Agreement on all renewals, with or without new money. As stated earlier, laws change and therefore, so do the terms on the Security Agreement (even though collateral description language may not change). It also eliminates any potential conflict over what collateral the Borrower/Debtor "intended" to secure the debt with. In addition, by signing the new Security Agreement, the Borrower/Debtor is confirming that they still own the collateral and have the right to pledge it (a circumstance that could change over time).
I wouldn't recommend getting a new Security Agreement on existing, unmatured loans just because the original was done five years (or more) ago without consulting your bank counsel.