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Percent accounts with balances is only one segment of util, which also includes overall and individual revolving and installment util.
Its exact weighting is unknown, but probably not huge.
New accounts to increase the denominator of the % with balance calculation will bring their own initial baggage, with inquiries, new accounts, and lowered AAoA.
I would not add new accts simply for that reason, as you already have a good mix of credit, unless you need them for other reasons, such as increased flexibility.