You can empty someone's bank roll today... NPC proxy won't help or hurt in that matter.
I'd rather have NPC proxy than Self.Balance as it's obviously more versatile and allows specific error handling.
Right now you can detect if something went wrong and retry X times, but that's the limit.
With NPC proxy you could tell exactly what went wrong and how to correct the problem, or alert the user if you can't.
If someone is pushing you, you could start a trasher or constantly step back to your position.
If you have low funds, you can alert the user.
If you haven't completed a quest you can alert the user / find an alternate route
Specific error handling is a must for advanced scripts, obviously common scripters don't need this, but some of us do.
Of all the feature requests, this is the one I want the most.