Now that fall is rolling around, it will not be as uncomfortable to wear one. Summer is a beast of a season to sport a vest, but the rest of the year is more tolerable.
It can't hurt.
I used to work nights at a junky little gas station many years ago. Never had any problems except the manager stealing cartons of smokes. I kind of liked the job. Lots of down time to sit around drinking coffee, read the paper, etc...
Make friends with the local cops. It's not hard, just be generous with the coffee and keep a fresh pot going at all times. Stale coffee is still stale, even at 4am. If you have a cruiser pulling in for a refill every 5-10min, badguys are probably going to look for a less risky target.
I like the Second Chance vest I have, but my experience is pretty skimpy. I haven't tried any other brands.