Is using uncited references in master thesis a good idea? Do you think uncited references can add extra value to a master thesis? 

If yes, what is the best way to include it in the master thesis? Maybe it can be mixed with the main references or can be listed in the appendix.
I would suggest avoiding adding references to your list of cited works if you do not cite those works. It may be appropriate to have a "Further Reading" section but this section may not be helpful in a master's thesis. Your thesis should ideally have a single, primary focus and therefore any additional content essentially serves as a distraction.

If you must include the references, cite them briefly.