Two things.
First, in regard to the OC target/deterrent conversation... I think there is a point to be made about the greater ease of access to your weapon when you OC. Personally, I normally only carry concealed. But if I know I'm going into a situation where I won't have much time to draw (like at a gas pump where somebody can walk up behind the pump and be 3 feet away before I see him) I make sure there's nothing to slow down my draw or cause me to fumble. Same goes for in the car, in a tight hallway, etc.
Second, as for reaction to an approaching beggar, my technique is similar to analog_kid. While taking a step or two back I say in a loud voice, "I don't want any trouble! Leave me alone! I don't have anything for you!"
I used to have a martial arts instructor who advised shouting that kind of phrase (e.g. "Don't hurt me!") regardless of whether you're scared. He saw it as as a sort of escalation of force that
1. frightens and embarrasses a BG
2. gets people (every potential witness within earshot) to look at you, backing away from BG and apparently really scared of him
3. helps you prove to a jury that you faced a determined assailant who couldn't be deterred save by force.