I've been working with CodeIgniter (http://codeigniter.com)lateley and in their latest version they added the capability to cache database query results. What they do is save the result object as a seliarized string in a file named like the md5 hash of the query.
Does Metabase support this feature also? if it doesn't, I think it would be cool to add it in a future release.
This is not provided as provided as part of Metabase because it can be used for other things besides caching queries.
Other than that, if you want to generate a page that is made of content taken from multiple database queries, it is more efficient to cache the actual HTML of the page, than keeping multiple caches for each query you performed.
These and other performance improvement aspects are explained Metabase FAQ: