Is Functional Encryption about Access Control over encrypted data alone? Informally, In functional encryption system , a decryption key allows a user to
learn a function of the encrypted data. But all i see is that the function acts as an access control over the data. 

Can we have richer functions, say can a user add two cipher texts and get the result in plain text using decryption key ? 

Are there any known forms of functional encryption schemes that allow anything else other than access control ?
Existing definitions for functional encryption don't support "combining" ciphertexts in the way that you suggest.

As far as doing more than just access control, two very recent papers (to appear next month at STOC 2013) achieve functional encryption for arbitrary functionalities:


Attribute-Based Encryption for Circuits by Gorbunov, Vaikuntanathan, Wee
Reusable Garbled Circuits and Succinct Functional Encryption by Goldwasser, Kalai, Popa, Vaikuntanathan &amp; Zeldovich


Two caveats:


These are feasibility results only, and are not practical (one could probably argue that they cannot be both practical and support arbitrary functionalities)
They achieve slightly relaxed (but still natural &amp; useful) security definitions for functional encryption, where either the number of keys or number of ciphertexts in the system is bounded (I don't remember the exact details).