Can I download the CPU, Network and Disk data from the graph tab?
Is it possible to download all the available data driving the plots on the graph page in the linode admin?
It's not possible to download the data that the graphs in the Linode Manager use. However, the data is the same as the resource usage data that you can collect from within your Linode with a monitoring utility such as top or cacti.
From there, most monitoring utilities can be configured or used with a script to output the data they collect to a file.
For example, there's a short guide on saving the output of the top utility to a file here.
While it doesn't provide a download, you can access the statistics via the new API. Specifically the getLinodeStats endpoint documentation may help