wow cool story, I would have done the same thing.
To answer the question. If I find money that can be traced back to its correct owner I will do so. Like finding a wallet or something like that. If its a 20 dollar bill lying in the road with no way of knowing where it came from I just pocket it and don't give it another thought. I think the most I have ever found was around $85 lying in the street at 1:00am after leaving a bar and walking thru a neighborhood to get to my car.
A cool story, my wife lost her wallet in Hawaii while on vacation. We got the wallet back a week later in the US mail with the money still in it. Nice people are out there.