For a Chartered Accountant in general, CPA will definitely be an added advantage if he/she is currently working in a US based MNC or India based MNC having substantial business operations in USA as CPA qualification will give knowledge of the US tax and regulatory compliance including US GAAP.
For a practising CA, CPA qualification might help him/her in getting work related to US Tax, Accounting & Payroll etc. for US based small & medium sized businesses and individuals. Many CA firms in India are taking up assignments from US in tax and accounting areas. They are simply associated with US based CPA firms for their outsourcing work. Apart from the outsourcing work as mentioned above, a CA with CPA as an additional qualification, can take up assignments of SOX audits of Indian clients.
Hence, opportunities are immense, only thing needed is, you have to make up your mind for such assignments.
All the best!!!!