Use urllib.quote_plus instead of urllib2.quote. The Nexto site uses + for spaces. The quote style (quote vs quote_plus) is going to be store dependent.
With the search results you really want to have the author and title be in the initial SearchResult object returned by the search function. Unfortunately, in this case you will need to use a second browser to accomplish this. See the Baen Webscription plugin for an example. I realize this will slow down the results but author and title are both very important. So much so that they are required to be retuned by the search function for all calibre bundled stores.
Other information such as DRM, cover... can be retrieved dynamically later by implementing the get_details function. See the Amazon plugin for an example. However, you have no need for get_details as you're already able to get everything in the search function. Aside from author which really should not be handled by get_details.
get_details is called sometime after the SearchResult is handed back to the search window and it is displaying the result. get_details is used to dynamically load more information about a result.