Best way to Improve live site and then push changes from dev to live? Currently I am applying a new Drupal theme on an existing site. 
I have created a separate instance for Development and copied the live site database and started working.

The new theme requires many new features ( modules, blocks, views etc ). I am just writing down every thing and of-course I need to redo it on live site once the theming is completed.

Is it possible that my Dev database gets updated automatically if changes are made on live site?

So once the theming is finished, I can drop the live DB and replace with Dev DB? Seems like a dream to me ..

Any help ?
Is it possible that my dev database gets updated automatically if changes are made on live site ?
So once the theming is finished, i can drop the live DB and replace with Dev one:) Seems like a dream to me ..

Databases shouldn't be migrated up (ie dev -&gt; prod), only down (ie prod -&gt; dev). If you migrate a database up, you will overwrite anything new on the production server. For example, any new accounts, comments, pages, or anything else that is in the database.
If you use the Features module, it will allow you to migrate some database settings as code (a features module) that can potentially solve your issue. Or if you are on D8, you can export configuration and import it in the other site.