I knew that would happen. For the most part, nyc cabbies are good people, and this is another example of it.
I'm curious about the two dudes you were supposed to meet however. Obviously they had your name and number, so someone you called about this decided to potentially set you up for something!
My only suggestion in the future is to realize that if this happens, don't go getting every municipal agency in NYC involved. At best, you will get a brush off, and at worst, two people call you to meet them in an alleyway.
It took a little time, but your guitar was never in danger of being stolen, and you got it back from the cabbie. In retrospect, the only people that needed to be involved in this were you and him (and the cab company). I understand you freaked out, but as a native NYC'er you should have been the first person to realize the cops don't give a crap about you, me or any other citizen, especially with a problem you had, which probably happens a hundred times a day. In fact, it's very possible they were the ones who set you up.....