Timed Item Spawn in MineCraft Chests

I'm looking to set up "incentives" for exploring different areas on my minecraft SMP server.

One idea I had was for items to spawn in chests scattered in out of the way areas that spawn harder to find items every certain interval if the chest is empty. So for example, a chest might spawn a diamond pick once every 48 hours if it doesn't already have a pick. (so a person doesn't happen upon a chest full of diamond picks)

Are there any bukkit plugins that support this, or some combination of plugins that would allow me to do this?

I've done a bit of research, and there's no mod exactly like the one you describe (which amazes me, it looks like a great idea!).

As for alternative approaches, I think you're best off using a shopping/economy mod, such as RealShop, which allows a chest to be set up as a 'shop', where players can put in 'currency', e.g. gold, and then take out as many of the item in the shop chest as they can afford.

By choosing the item you use as currency carefully (and by carefully setting prices) you can get a similar 'exploration reward' system set up.