A very nice article about long-period variables has been prepared for the distinguished book series “Annual Reviews of Astronomy and Astrophysics” by Dorota Skowron and Igor Soszynski. This includes a broad historical background as well as discussion of the importance of these types of stars for various astronomy problems still to be explored.
It would be well worth reading as regards the types of data that should be acquired and the role of long-term surveys in this regard.
The astro-ph preprint is linked from here:
\Brian