Should I negotiate my severance? after 13 years as a copywriter

My manager said the package is final, but the letter gives me time to review. I am in Spokane, in case local advice matters. There is a non-disparagement clause. Should I see a lawyer?

An hour with an employment lawyer cost me a small fee and made me feel much safer about signing.

I asked for two more weeks and a neutral reference. They agreed to the reference and added a week.