Before rewarding for destroying a spawner, it would be nice if you checked for cancelled events. We have spawners that are WorldGuarded (not by design, but circumstance). When someone destroys the block, they are given the reward, but the block is not destroyed (since WG cancels it). If your priority is monitor (which it should be since you don't cancel events), you'll always know if a plugin has cancelled it (for example, modifyworld, residence, or worldguard).

As it stands, a player can destroy a protected spawner over and over again and completely destroy the economy.

I see in your code that you actually do check for cancelled events and are on monitor priority, so sorry for not looking first.
However, its still giving rewards for destroying spawners in protected areas

I have only tested with WG. Do you know what other region plugin is causing this issue?

WG. I defined a region, made sure I couldn't build in it, and when I break the spawner (which is cancelled), I get the money. I'm using the 0.0.9c from 2 Jan.
Screenshot of this:
http://dl.dropbox.com/u/122940/MC/2012-01-29_20.33.45.png

Okay, I just compiled your code here, and it behaves correctly. However the compiled version on bukkitdev does not. Can you recompile and update the bukkit dev version??

Yup, your timing is uncanny. I'm prepping an update that should go up tonight. Thanks for your input.

New version posted on dev bukkit.