how difficult is it to extend a single entry L visa, that is valid for 30 days, for another 30 days

Lewis, as long as you prepare the required documents, it is not that difficult to extend the tourist L type. There is no special criterion. The consular officers will decide if you can get the extension according to your situation.
You should prepare those documents first including your passport, valid registration form of temporary residence, a filled-out application form attached with a half-length color photo, hotel reservation and the return ticket.
And then submit the application to the exit and entry administration to extend it.

Thanks for your very quick response Louis . I want to stay to do some more sightseeing. Do they see this as a valid reason or do they require special circumstances before they will issue the extension.

They may see that as a valid reason. If you can provide travel itinerary, I think you can probably get the extension.