For the half an hour, I would say it's not worth it. The rule of the road is:- If you leave extra time for the journey, you won't need it. If you leave ten minutes late you will meet the milk float stopped in a one way sreet / tractor in a country lane / etc.!
1) Get there three hours early.
2) Check in easily, whilst others are clamouring for special treatment because they are late (and note that the excuse they give is never their fault
).
3) Buy a paper or magazine.
4) Find a quiet-ish corner and read, take tea. Watch the world go by and then ...
5) Walk in a relaxed manner to the gate.