“If the cost of automating the accounting for transactions in the ERP system exceeds the benefit of cost savings, is it worth investing?

iif we want to adopt any new module related to accounting system or internal control should be cost benefit analysis so it is not worth investing because the cost exceed benefit.

but sure the adopt for ERP system it will be cost saving except if you speak about very small entity

Though the automation cost exceeds the cost savings it is very much worth to invest in automation since the organization is based on going concern.  In the long run will help the business more cost saving with better internal controls features