I'v earned a bunch of dog tags. Just wondering if selecting them has any affect on the game (upgrades, super powers, etc.) or if their all there for show only? Thanks.

They don't have any effects. They're just for show-off purposes

So there is absolutely no need to collect them, run away from sweet spot?

As Jonki said, it's just for show off purposes.
"I use this dogtag, because I have this award unlocked" or... "I'm from this country" or... well, you get the idea.