Should an elevated strep. Titer be treated with antibiotics?

No. This means your child had a previous strep infection and had an immune respone which is a good thing. The elevation does tell us when the infection was active. So rely on what symptoms your child has and ask advice of your doctor. If your child is sick and has a positive throat culture, yes antibiotics are needed.
Probably not. Elevated strep titers such as aso usually mean previous exposure rather than current infection.