Individually, not anything game changing. If they do stack, and some do - they can definitely help. The problem is there is no real data or response from Relic on which do (I think).
all bulletins stack. I'm sure i seen a reply from Relic on the COH2 site forums about it.
Lately in 4v4 games US games, i have pushed with rears while building tank traps for green cover. If you can push far enough, putting tank traps up messes with the enemy vehicle pathing.