I was assaulted and punched in mustache area of face resulting in a minor scar however it is a scar. How much is smthing like that worth to sue?

It depends on the size and shape of the scar, how you looked before the scar (on a model a small scar would likely generate recovery of a far greater amount of damages than it would be worth for an average person), any financial impact on your ability to generate income, the cost of medical care, lost wages, etc. 

In addition, being punched in the face can produce very different results if the punch was in a fight you started, or that both of you agreed to, or was thrown without provocation.

A punch is usually an intentional tort and to discourage anti-social behavior courts can award punitive damages against the wrongdoer.

A scar is not a route to riches. One ever-present issue is whether the defendant has assets -- if he does not you can't get blood from a stone or money from someone who has nothing.

Even if the guy who punched you has insurance that will pay a judgment (and often intentional tors are excluded from coverage) you'll probably get nothing unless you are represented by a lawyer as insurance companies (who often have to defend their insured anyway) make mincemeat of people who are acting pro se.

Finally, there usually is a very short statute of limitations -- so unless you act quickly and file suit, the claim would be time barred.